3. The Periodic Table and Electron Configuration

Question 1

Periodic Table

Answer 1

• an arrangement of information for each known element into a table
• a graphical classification of information for each known element
• for each element, the name, symbol, atomic number + atomic weight is given

Question 2

Period

Answer 2

• a horizontal row of elements in the periodic table
• there are seven periods
• the number of elements in each period corresponds to the number of electrons allowed in the valence shell

Question 3

Family

Answer 3

• also known as a group
• a column of elements in the periodic table
• have a similar electron configuration
• have the same electron configuration in the outermost energy level (valence shell)
• have the same general chemical properties
• show a gradation in physical properties

Question 4

Periodic Law

Answer 4

• when the elements are arranged in order of increasing atomic number, there is a periodic recurrance of properties

Question 5

Main-group element

Answer 5

• an element in the A groups of the periodic table 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A

Question 6

Transition elements

Answer 6

• an element in the B groups of the periodic table 3B, 4B, 5B, 6B, 7B, 8B, 1B, 2B

Question 7

Inner Transition elements

Answer 7

• an element in the two rows of elements outside the body of the periodic table

Question 8

Metals

Answer 8

• make up the majority of the elements
• solid at room temperature, except mercury
• shiny
• conduct electricity
• ductile
• malleable
• form alloys: a solution of one or more metals dissolved in another metal
• most distinguishing characteristic is their tendency to transfer or lose electrons in chemical reactions

Question 9

Non metals

Answer 9

• 18 elements, all but hydrogen are on the right side of the periodic table
• do not conduct electricity
• most distinguishing characteristic is their tendency to share or gain electrons in chemical reactions

Question 10

Metalloids

Answer 10

• 6 elements
• display some of the properties of metals and some of non metals
• have a metallic lustre, but do not transfer electrons in chemical reactions
• most distinguishing characteristic is the property of semi conduction

Question 11

Alkali metals

Answer 11

• group 1A elements in the periodic tabl
• react with water to give hydrogen gas and a metal hydroxide, MOH, where M is the metal

Question 12

Alkaline earth metals

Answer 12

• group 2A elements in the periodic table

Question 13

Halogens

Answer 13

• group 7A elements in the periodic table
• all halogens are coloured substances, with the colour deepening down the table
• X is a commonly used symbol for halogens
• all halogens form compounds with sodium with the general formula NaX

Question 14

Noble gases

Answer 14

• group 8A elements in the periodic table
• boiling points increase going from top to bottom of the group

Question 15

Electron configuration or structure

Answer 15

• the distribution of electrons in the orbitals of an atom

Question 16

Ground state

Answer 16

• the electron configuration of the lowest energy state of an atom

Question 17

Electron shell

Answer 17

• a region of space around the nucleus of an atom that contains electrons that have approximately the same energy level
• electrons within an electron shell spend most of their time at approximately the same distance from the nucleus
• electrons in the first shell, closest to the nucleus, are held most strongly by it and therefore are the hardest to remove. They are said to be the lowest in energy
• electrons in higher numbered shells, further from the nucleus, are less strongly held and are easier to remove. These are said to be higher in energy.

Question 18

Electron sub-shell

Answer 18

• a region of space within an electron shell that contains electrons that have the same energy level
• s sub-shell accommodates 2 electrons
• p sub-shell accommodates 6 electrons: one orbital along each of the x, y and z axes
• d sub-shell accommodates 10 electrons
• f sub-shell accommodates 14 electrons

Question 19

Electron orbital

Answer 19

• a region within an electron sub-shell where an electron is most likely to be found
• each orbital has a specific shape and holds a maximum of two electrons with paired spins
• s orbitals have the shape of a sphere
• p orbitals have the shape of a dumbell

Question 20

The pairing of electron spins

Answer 20

• a spinning electron generates a tiny magnetic field
• when the magnetic fields of two electrons are aligned N-S the electron spins are paired

Question 21

Valence shell

Answer 21

• the outermost occupied shell of an atom

Question 22

Valence electron

Answer 22

• an electron occupying the valence shell of an atom

Question 23

Rules for electron configuration

Answer 23

1. Orbitals fill in the order of increasing energy ie. inner to outer
2. Each orbital accommodates up to two electrons with paired spins ie. the electrons spin in opposite directions
3. In the case of orbitals of equal energy, each orbital is half filled before any are completely filled

Question 24

Order of orbital fullfillment

Answer 24

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p

Question 25

Elements in the same group have the same ground state electron configuration in their valence shell.

Answer 25

All main group elements have s or p orbitals being filled.

Question 26

Transition elements have d orbitals being filled.

Answer 26

Inner transition elements have f orbitals being filled.

Question 27

Atomic size

Answer 27

• determined by the size of the outermost occupied orbital
• increases going down a group as electrons occupy successive shells and orbitals
• decreases from left to right across a period as the electrons occupy the same shell and therefore are the same distance from an increasingly positive nucleus. With each additional proton, the nucleus exerts an increasingly stronger pull on the valence electrons and therefore the atomic radius decreases
• an example of the periodicity of a physical property

Question 28

Ionization energy

Answer 28

• the energy required to remove the most loosely held electron (valence electron) from an atom in the gas phase
• the higher the ionization energy, the more difficult the electron is to remove
• increases going up a group as the outer electrons are closer to the nucleus and are therefore held more tightly. Also, going down a group, the outer electrons are shielded from the positive force of the nucleus by the electrons in the inner shells. The greater the shielding, the lower the ionization energy
• increases from left to right across a period. With the addition of each proton, the nucleus exerts increasing force on the outer shell of electrons
• an example of periodicity of a chemical property

Question 29

2nd ionization energy

Answer 29

• the energy required to remove the second valence electron

Question 30

Lewis dot structure

Answer 30

• a diagramatic representation of an atom or ion showing the arrangement of the valence electrons
• the symbol of the element is surrounded by a number of dots equal to the number of valence electrons

Question 31

Orbital box diagram

Answer 31

• a graphical representation using boxes and arrows to describe the electron configuration of an atom
• each orbital is represented by a box
• a single electron in an orbital is represented by an arrow with its head up in the respective orbital box
• two electrons in an orbital are represented by two arrows with heads at opposite ends in the respective orbital box

Question 32

Noble gas notation

Answer 32

• an alternative method of writing ground state electron configurations
• the symbol for the noble gas preceding the particular atom is noted in brackets to indicate the electron configuration of all filled shells. This is immediately followed by the notation to indicate the valence electron configuration.