We are now in a position to consider the arrangements of electrons in atoms. The way in which the electrons are distributed among the various orbitals of an atom is called its electron configuration. The most stable, or ground, electron configuration of an atom is that in which the electrons are in the lowest possible energy states. If there were no restrictions on the possible values for the quantum numbers of the electrons, all the electrons would crowd into the 1s orbital because it is the lowest in energy (Figure 6.24). The Pauli exclusion principle, however, tells us that there can be at most two electrons in any single orbital. Thus, the orbitals are filled in order of increasing energy, with no more than two electrons per orbital. For example, consider the lithium atom, which has three electrons. (Recall that the number of electrons in a neutral atom is equal to its atomic number, Z.) The 1s orbital can accommodate two of the electrons. The third one goes into the next lowest energy orbital, the 2s.
We can summarize any electron configuration by writing the symbol for the occupied subshell and adding a superscript to indicate the number of electrons in that subshell. For example, for lithium we write 1s22s1 (read "1s two, 2s one"). We can also show the arrangement of the electrons as:
In this kind of representation, which we will call an orbital diagram, each orbital is represented by a box and each electron by a half arrow. A half arrow pointing upward represents an electron with a positive spin quantum number (ms = ), and a downward half arrow represents an electron with a negative spin quantum number (ms = ). This pictorial representation of electron spin is quite convenient. In fact, chemists and physicists often refer to electrons as "spin-up" and "spin-down" rather than specifying the value for ms.
Electrons having opposite spins are said to be paired when they are in the same orbital. An unpaired electron is not accompanied by a partner of opposite spin. In the lithium atom the two electrons in the 1s orbital are paired, and the electron in the 2s orbital is unpaired.
Periods 1, 2, and 3
It is informative to consider how the electron configurations of the elements change as we move from element to element across the periodic table. Hydrogen has one electron, which occupies the 1s orbital in its ground state:
The choice of a spin-up electron here is arbitrary; we could equally well show the ground state with one spin-down electron in the 1s orbital.
The next element, helium, has two electrons. Because two electrons with opposite spins can occupy an orbital, both of helium's electrons are in the 1s orbital:
The two electrons present in helium complete the filling of the first shell. This arrangement represents a very stable configuration, as is evidenced by the chemical inertness of helium.
The electron configurations of lithium and several elements that follow it in the periodic table are shown in Table 6.3 . For the third electron of lithium, the change in principal quantum number represents a large jump in energy and a corresponding jump in the average distance of the electron from the nucleus. It represents the start of a new shell of electrons. As you can see by examining the periodic table, lithium starts a new row of the periodic table. It is the first member of the alkali metals group (1A).
The element that follows lithium is beryllium; its electron configuration is 1s22s2 (Table 6.3). Boron, atomic number 5, has the electron configuration 1s22s22p1. The fifth electron must be placed in a 2p orbital because the 2s orbital is filled. Because all the three 2p orbitals are of equal energy, it doesn't matter which 2p orbital is occupied.
With the next element, carbon, we encounter a new situation. We know that the sixth electron must go into a 2p orbital. However, does this new electron go into the 2p orbital that already has one electron, or into one of the others? This question is answered by Hund's rule, which states that for degenerate orbitals, the lowest energy is attained when the number of electrons with the same spin is maximized. This means that electrons will occupy orbitals singly to the maximum extent possible, with their spins parallel. Thus, for a carbon atom to achieve its lowest energy, the two 2p electrons will have the same spin. In order for this to happen, the electrons must be in different 2p orbitals, as shown in Table 6.3. We see that a carbon atom in its ground state has two unpaired electrons. Similarly, for nitrogen in its ground state, Hund's rule requires that the three 2p electrons singly occupy each of the three 2p orbitals. This is the only way that all three electrons can have the same spin. For oxygen and fluorine, we place four and five electrons, respectively, in the 2p orbitals. To achieve this, we pair up electrons in the 2p orbitals, as we will see in Sample Exercise 6.7.
Hund's rule is based in part on the fact that electrons repel one another. By occupying different orbitals, the electrons remain as far as possible from one another, thus minimizing electron-electron repulsions.
The filling of the 2p subshell is complete at neon (Table 6.3), which has a stable configuration with eight electrons (an octet) in the outermost shell. We next encounter sodium, atomic number 11, marking the beginning of a new row of the periodic table. Sodium has a single 3s electron beyond the stable configuration of neon. We can abbreviate the electron configuration of sodium as follows:
The symbol [Ne] represents the electron configuration of the 10 electrons of neon, 1s22s22p6. Writing the electron configuration in this manner helps focus attention on the outermost electrons of the atom. The outer electrons are the ones largely responsible for the chemical behavior of an element. For example, we can write the electron configuration of lithium as:
By comparing this with the electron configuration for sodium, we can appreciate why lithium and sodium are so similar chemically: They have the same type of outer-shell electron configuration. All the members of the alkali metal group (1A) have a single s electron beyond a noble-gas configuration. Electrons in subshells not occupied in the nearest noble-gas element of lower atomic number are referred to as outer-shell electrons, or valence electrons. The electrons in the inner shells are the core electrons.
SAMPLE EXERCISE 6.7
Draw the orbital diagram representation for the electron configuration of oxygen, atomic number 8.
SOLUTION Figure 6.24 shows the ordering of orbitals. Two electrons each go into the 1s and 2s orbitals. This leaves four electrons for the three 2p orbitals. Following Hund's rule, we put one electron into each 2p orbital until all three have one each. The fourth electron is then paired up with one of the three electrons already in a 2p orbital, so that the correct representation is
The corresponding electron configuration is written 1s22s22p4 or [He]2s22p4. The 1s2 or [He] electrons are the inner-shell, or core, electrons of the oxygen atom. The 2s22p4 electrons are the outer-shell, or valence, electrons.
Write the electron configuration of phosphorus, element 15.
Answer: 1s22s22p63s23p3 = [Ne]3s23p3
Period 4 and Beyond
The noble-gas element argon marks the end of the row started by sodium. The configuration for argon is 1s22s22p63s23p6. The element following argon in the periodic table is potassium (K), atomic number 19. In all its chemical properties, potassium is clearly a member of the alkali metal group. The experimental facts about the properties of potassium leave no doubt that the outermost electron of this element occupies an s orbital. But this means that the highest-energy electron has not gone into a 3d orbital, which we might have expected it to do. Here the ordering of energy levels is such that the 4s orbital is lower in energy than the 3d (Figure 6.24).
Following complete filling of the 4s orbital (this occurs in the calcium atom), the next set of equivalent orbitals to be filled is the 3d. (You will find it helpful as we go along to refer often to the periodic table on the front inside cover of the text.) Beginning with scandium and extending through zinc, electrons are added to the five 3d orbitals until they are completely filled. Thus, the fourth row of the periodic table is 10 elements wider than the two previous rows. These 10 elements are known as transition elements or transition metals. Note the position of these elements in the periodic table.
In accordance with Hund's rule, electrons are added to the 3d orbitals singly until all five orbitals have one electron each. Additional electrons are then placed in the 3d orbitals with spin pairing until the shell is completely filled. The orbital diagram representations and electron configurations of two transition elements are as follows:
Upon completion of the 3d transition series, the 4p orbitals begin to be occupied until the completed octet of outer electrons (4s24p6) is reached with krypton (Kr), atomic number 36, another of the noble gases. For the elements of this fourth row of the table, the 4s, 3d, and 4p electrons are considered the valence, or outer-shell electrons.
Rubidium (Rb) marks the beginning of the fifth row. Refer again to the periodic table on the front inside cover of the text. Notice that this row is in every respect like the preceding one, except that the value for n is 1 greater. The sixth row of the table begins similarly to the preceding one: one electron in the 6s orbital of cesium (Cs) and two electrons in the 6s orbital of barium (Ba). The next element, lanthanum (La), represents the start of the third series of transition elements. But with cerium (Ce), element 58, a new set of orbitals, the 4f, enters the picture. The energies of the 5d and 4f orbitals are very close. For lanthanum itself, the 5d orbital energy is just a little lower than the 4f. However, for the elements immediately following lanthanum, the 4f orbital energies are a little lower, so that the 4f orbitals fill before the 5d orbitals.
There are seven equivalent 4f orbitals, corresponding to the seven allowed values of ml, ranging from 3 to -3. Thus it requires 14 electrons to fill the 4f orbitals completely. The 14 elements corresponding to the filling of the 4f orbitals are elements 58 to 71, known as the lanthanide (or rare earth) elements. To avoid making the periodic table unduly wide, the lanthanide elements are set below the other elements. The properties of the lanthanide elements are all quite similar, and they occur together in nature. For many years it was virtually impossible to separate them from one another.
After the lanthanide series, the third transition element series is completed, followed by the filling of the 6p orbitals. This brings us to radon (Rn), heaviest of the noble-gas elements. The final row of the periodic table begins as the one before it. The actinide elements, of which uranium (U, element 92) and plutonium (Pu, element 94) are the best known, are built up by completion of the 5f orbitals. The actinide elements are radioactive, and most of them are not found in nature.
Incomplete combustion takes place when there is not enough oxygen to allow the fuel to react completely and burn in order to produce carbon dioxide and water. For example, the yellow flame of a burning candle is due to the presence of unburnt carbon particles that are hot and emit a yellow light.What is Flame Class 8 short? ›
Answer: Flame is a region where the burning or combustion of gaseous substances take place.What is life process Class 10 short answer? ›
Solution: Life processes such as respiration, digestion, excretion, circulation and transportation are essential for maintaining life.How do we get the supply of carbon dioxide Class 8 science? ›
(a) Carbon dioxide gas is formed, when a fuel burns in sufficient supply of air. (b) Carbon monoxide gas is formed, when a fuel burns in insufficient supply of air.Why did the flame was putting off? ›
Carbon dioxide molecules are heavier than air. Because of this, they push the oxygen and other molecules in the air out of the way as they sink down over the flame and candle. When oxygen is pushed away from the wick, it can't react with the wax anymore. This makes the flame go out.Why candle is catch on fire? ›
Candle fires are more likely with high fragrance content. high fragrance content. It is not unknown for customers to add essential oils to 'boost' a candle. Sustainers Candle fires sometimes occur when the flame reaches the bottom of the container and the small amount of wax remaining is heated to higher temperatures.What is calorific value of fuel? ›
Calorific value is defined as the amount of heat energy released during complete combustion of a unit mass of a fuel. It is expressed in kJ/kg.Is coal a Class 8? ›
Coal is a fossil fuel, that was formed by the decay of vegetation, which existed millions of years ago. It is a non-crystalline form of carbon. Carbonisation: The slow process of conversion of dead vegetations into coal is called carbonisation.How does CO2 control fire? ›
CO2 being heavier than oxygen, covers the fire like blanket and also brings down the temperature of fuel. Since, contact between the fuel and oxygen is cut off the fire comes under control.What are the 4 main life processes? ›
The basic processes of life include organization, metabolism, responsiveness, movements, and reproduction.
Life processes: These are the 7 processes all living things do - movement, reproduction, sensitivity, nutrition, excretion, respiration and growth.What are the 11 life processes? ›
- Ingestion. To take in/ eat.
- Digestion. Mechanical: chewing. ...
- Absorption. Intestines: break down(smallest unit a cell can use, GLUCOSE) ...
- Cellular respiration-cell. Mitochondria coverts glucose into energy ->ATP.
- Assimilation. Build.
- Excretion. Getting rid of liquid and gas.
- Egestion. ...
Carbon dioxide is incombustible and also does not support burning. Hence, it is used in fire extinguisher. When sprayed on burning object it stops the supply of oxygen and extinguishes fire.What are the 3 ways in which CO2 is transported? ›
There are three means by which carbon dioxide is transported in the bloodstream from peripheral tissues and back to the lungs: (1) dissolved gas, (2) bicarbonate, and (3) carbaminohemoglobin bound to hemoglobin (and other proteins).Why is CO2 a good fire extinguisher 8? ›
fires require oxygen to maintain combustion, and carbon dioxide displaces the oxygen feeding the fire.Why do flames always face up? ›
Basically the continuous movement of hot air going up displaces cooler air down to the side which then gets heated up again and move upwards causing the distinctive shape of the flame and which is why it points only upwards.What happens to fire in wind? ›
Wind speed is the environmental variable that has the most significant effect on the spread of fires. With wind speeds below around 10 km/hour, a fire will usually burn slowly without a definite spread direction. However, as winds increase in strength, the rate of fire spread increases.Why did the candle melt? ›
About one-quarter of the energy from combustion is emitted as heat. The heat maintains the reaction, vaporizing wax so that it can burn, melting it to maintain the supply of fuel. The reaction ends when there is either no more fuel (wax) or when there isn't enough heat to melt the wax.Is candle wax toxic? ›
Candle wax is considered nonpoisonous, but it may cause a blockage in the intestines if a large amount is swallowed. A person who is allergic to the scent or color ingredients in the candle may have an allergic reaction from touching the candle.Are candles safe? ›
Lead wicks aside, burning candles can expose you to potentially hazardous chemicals, such as formaldehyde, acetaldehyde, and acrolein. Though these chemicals can be dangerous, studies conclude that exposure to these chemicals when burning candles is too low to present a direct health hazard.
The National Candle Association recommends using a candle snuffer or some sort of lid to extinguish a candle. The organization says using water can cause hot wax to splatter, which is one way an explosion can occur.What is the SI unit of calorific value? ›
The SI unit of calorific value is J/kg since calorific value is heat produced when 1 kg of fuel is burnt.Which fuel has high calorific? ›
LPG has the highest calorific value. LPG has a typical specific calorific value of 46100 kJ/kg. The calorific value of a fuel may be defined as the amount of heat energy (kJ) produced by complete combustion of 1 kg of fuel under the standard conditions.What is the unit of calorific value? ›
The SI unit of calorific value is J kg - 1 .What are the 4 class of fire? ›
Class A – fires involving solid materials such as wood, paper or textiles. Class B – fires involving flammable liquids such as petrol, diesel or oils. Class C – fires involving gases. Class D – fires involving metals.Is tar a fossil fuel? ›
Fossil fuels include coal, petroleum, natural gas, oil shales, bitumens, tar sands, and heavy oils.What is a natural fuel? ›
Natural Gas Fuel Basics. Like fossil-derived natural gas, renewable natural gas—which is produced from decaying organic materials—must be compressed or liquefied for use as a transportation fuel. Natural gas is an odorless, gaseous mixture of hydrocarbons—predominantly made up of methane (CH4).How do forest fires increase CO2? ›
Burning of vegetation due to forest fires leads to combustion of carbon stored in trees which is released in the atmosphere. Potent and detrimental gases like CO2and methane (CH4) escape into the atmosphere.Why does CO2 Turn off fire? ›
Carbon dioxide extinguishes work by displacing oxygen, or taking away the oxygen element of the fire triangle. The carbon dioxide is also very cold as it comes out of the extinguisher, so it cools the fuel as well.What is a CO2 fire extinguisher used for? ›
CO2 fire extinguishers are mainly aimed at electrical fires but are also suitable for Class B liquid fires and are used in different ways depending on the type of fire they are being used on. Do not use CO2 extinguishers in small rooms as CO2 gas is poisonous at only 4% concentration and can kill at just 8%.
Sand, wood and glass are all non-living things.Do humans carry out all 7 life processes? ›
There are seven essential processes in common: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition or MRS GREN. 3. Does all living things exhibit MRS GREN? Yes, anything that is alive (animals, plants, humans) MUST demonstrate all seven of these processes!!Is a Butterfly a living thing? ›
An everyday example is that students think various lifecycle stages of a butterfly are not alive (the eggs and immobile pupae), whereas a caterpillar and butterfly can move and are therefore considered to be alive.Is the virus alive or dead? ›
So were they ever alive? Most biologists say no. Viruses are not made out of cells, they can't keep themselves in a stable state, they don't grow, and they can't make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.Can a fire reproduce? ›
Although you could argue to some extent that fire has the ability to grow, change, consume energy, and respond to stimuli, it certainly does not contain cells or reproduce.Is fire a living? ›
People sometimes think fire is living because it consumes and uses energy, requires oxygen, and moves through the environment. Fire is actually non-living. A reason why is it cannot eat or breath. Fire can spread quickly and burn.What are the 5 types of life? ›
Living things are divided into five kingdoms: animal, plant, fungi, protist and monera.Is plant a living thing? ›
Plants are living things. Plants are born and grow. Some plants, like geraniums, grow very quickly. Others, like oak trees, grow very slowly.Is fire alive Mrs Gren? ›
Fire is non-living but judge it with MRS GREN with your 11 year old child hat on and it might not be so clear: Movement – fire spreads. Respiration – fire consumes oxygen (not visible but might be prior knowledge) Sensitivity – when you blow on fire it moves.Is CO2 clean agent? ›
Carbon dioxide (CO2) is another extinguishing agent with all the properties of a clean agent but is often classified differently due to the dangers associated with it. Here we will review the different types of gaseous fire protection systems and how they work.
There are different options - a wood fire, a gas fire or an electric fire. Discover what suits you best.Which gas catches fire fast? ›
The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. Examples of inflammable substances are petrol, alcohol, Liquified Petroleum Gas (LPG) etc.How does CO2 change pH? ›
When CO2 is dissolved in water, a part of it reacts with water to become carbonic acid (H2CO3). It is the hydrogen ions present in carbonic acid that make water acidic, lowering the pH.Does plasma carry urea? ›
Transporting substances in plasma
Plasma is made primarily of water. Many of the molecules the body needs to transport, such as urea , carbon dioxide and glucose, are soluble in water. This means that a large number of substances can be transported around the body in plasma at any one time.
Oxygen is carried in the blood in two forms: (1) dissolved in plasma and RBC water (about 2% of the total) and (2) reversibly bound to hemoglobin (about 98% of the total).Why can't you use a CO2 fire extinguisher on wood? ›
Dangers: CO2 extinguishers should not be used on fires involving solid materials, such as paper, wood and fabric, and also are not suitable for use on flammable gases. How it works: The CO2 works by cutting off the fire's oxygen supply. This then smothers it and, as it does so, extinguishes the flames.How often should you replace CO2 in fire extinguisher? ›
The maintenance schedule varies by type of extinguisher: Water, foam and powder extinguishers have to be discharged and refilled every five years. CO2 extinguishers must be refurbished every 10 years.Why is oxygen not used in fire extinguishers? ›
CO2, being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled. Therefore, CO2 is used in fire extinguishers.How does air affect a flame? ›
Oxygen. Air contains about 21 percent oxygen, and most fires require at least 16 percent oxygen content to burn. Oxygen supports the chemical processes that occur during fire. When fuel burns, it reacts with oxygen from the surrounding air, releasing heat and generating combustion products (gases, smoke, embers, etc.).Will a candle burn if no oxygen is present? ›
Most of the fires that we see in everyday life are carbon combustion: campfires, oven flames, candle flames, barbecue grills, forest fires, gas furnaces, gasoline burning in engines, etc. The key to remember is that carbon combustion requires oxygen. As soon as there is no oxygen left, carbon combustion stops.
It needs oxygen. If you could look down into the flame, you'd see that oxygen molecules from the air interact with wax molecules and have a chemical reaction. And the products of the reaction, that means the stuff that's produced, is water vapor, carbon dioxide gas, and heat, and light.Is air needed for a candle to burn? ›
Oxygen is necessary for every burning process, whether burning a candle, or burning food at a cellular level*. When all the oxygen in the jar is used, the candle flame can no longer burn and so expires.
When a burn occurs to the skin, nerve endings are damaged causing intense feelings of pain. Every year, millions of people in the United States are burned in one way or another. Of those, thousands die as a result of their burns.What is the hottest color of fire? ›
The hottest part of the flame is the base, so this typically burns with a different colour to the outer edges or the rest of the flame body. Blue flames are the hottest, followed by white. After that, yellow, orange and red are the common colours you'll see in most fires.Can fire burn itself? ›
The actual flames of the fire are the release of some of the heat energy as light. These components have led to the development of the 'fire triangle' of fuel, oxygen and heat. Remove any one of these and fire cannot sustain itself.Is the sun fire? ›
The Sun does not "burn", like we think of logs in a fire or paper burning. The Sun glows because it is a very big ball of gas, and a process called nuclear fusion is taking place in its core.Can you burn pure oxygen? ›
The technical reality is that the oxygen doesn't burn,” said Mark Bruley, vice president for accident and forensic investigation at ECRI Institute. “It's a subtlety of the physics of fire. Oxygen makes other things ignite at a lower temperature, and burn hotter and faster. But oxygen itself does not catch fire.”Are Stars on fire? ›
with stars, they are not actually on fire. The heat and light are released by the chemical process of atoms joining together. This middle stage in the life cycle of a star is called the main sequence. As the hydrogen is used up, the star begins to fuse helium and heavier elements.Why does the sun never burn out? ›
The Sun survives by burning hydrogen atoms into helium atoms in its core. In fact, it burns through 600 million tons of hydrogen every second. And as the Sun's core becomes saturated with this helium, it shrinks, causing nuclear fusion reactions to speed up - which means that the Sun spits out more energy.Why shouldn't you let candles burn for more than 4 hours? ›
If you burn your candle for more than 4 hours at a time, carbon will collect on the wick, and your wick will begin to "mushroom." This can cause the wick to become unstable, the flame to get too large, your candle to smoke, and soot to be released into the air and around your candle container.
Initially, the candle burns by making use of the oxygen within the glass and slowly when there is no oxygen the flame goes off. Which candle goes out first? The candle that is the shortest will go out first. It is because the CO2 is denser than air so it will settle down at the bottom eventually putting off the fire.Why should you never burn a candle for more than 4 hours? ›
Burning a candle for too long will cause carbon to collect on the wick, leading it to “mushroom.” The wick will then become unstable and produce a dangerously large flame. Plus, your candle will start to smoke and release soot. Avoid this by always following the manufacturer's instructions.