The Periodic Table

Question 1

Who’s attempt at classification became the basis for todays modern periodic table and how is it arranged?

Answer 1

• Dmitri Mendeleev

* He arranged the elements in order of relative atomic mass

Question 2

Who showed that the order of elements in the peripdic table could be more accurately related to atomic number?

Answer 2

Henry Mosely

Question 3

What are the horizontal rows of elements in the periodic tables?

Answer 3

They are called periods and are numbered to 1 to 7. These correspond to the electron shells.

Question 4

What are the vertical columns in the periodic table?

Answer 4

They are called groups. They are named 1-0

Question 5

What is similar between all elements in a group in regard to electrons?

Answer 5

All the elements in a particular group have the same number of electrons in their outermost sub-shell. This characterises the group

Question 6

What is the total number of electrons in the outer shell the same as?

Answer 6

The element’s group number

Question 7

The period table is divided into groups according to what?

Answer 7

Which sub-shell is being filled

Question 8

What block are group 1 and 2 elements in?

Answer 8

They are s block elements because electeons are being added to s sub-shells

Question 9

What group are the p block elements?

Answer 9

Groups 3 to 0

Question 10

What are the d block elements?

Answer 10

The ones in the middle including the transition metals

Question 11

What are the f block elements?

Answer 11

The lanthanide and actinide elements (at the bottom of the periodic table)

Question 12

What is periodicity?

Answer 12

The repeating patterns found along a period. E.g:

• moving across a period, each element has an atomic number one greater than the previous element
• successive elements have one more proton and one more electron in their atoms
• this gradual change produces trends in both physical and chemical properties of the elements

Question 13

What is the atomic radius?

Answer 13

The distance from the centre of the atom to its outermost electrons

Question 14

What is the covalent radius?

Answer 14

Half the shortest distance from one nucleus to the next in a covalently bonded molecule

Question 15

What is the metallic radius?

Answer 15

Half the shortest distance from one metal ion nucleus to the next

Question 16

What happens with atomic radius’ as you go down a group?

Answer 16

The number of electrons increases and so does the size of the atom and the atomic radius

Question 17

What is the overall trend in atomic radius along a period?

Answer 17

• It decreases.
• All of the outer electrons in a period have the same amount of inner shells shielding the nuclear charge.
• Moving across the period, a proton is added to the nucleus of each element. An electron is also added but it goes into the same shell and the positive charge charge acts over a definitive area
• this increasing positive nuclear charge pulls with a greater force on the negative electrons. All the electron shells are drawn closer to the nucleus so the atomic radius decreases

Question 18

What is the first ionisation energy?

Answer 18

The energy required to remove one mole of the outermost electrons from one mole of atoms of an element in the gaseous state

Question 19

What do first ionisation energies depend on?

Answer 19

• the charge of the nucleus
• the distance of the outer electrons from the nucleus
• the shielding by inner electron shells
• whether the electron is alone in an orbital, or one of a pair

Question 20

What happens with first ionisation energies in period 3?

Answer 20

• overall first ionisation energies increase because more energy is needed to remove an electron moving across the period because as the number of protons increases, the positive charge on the nucleus increases. The force of attraction on the electrons increases
• there is a dip in the first ionisation energy of aluminium because the first electron is taken from the 3p sub-shell. This electron is at a higher energy level than those in the 3s sub-shell so is easier to remove
• then there is another dip at sulfur as the first paired electron is removed. Paired electrons repel each other; there is more electrostatic repulsion and it is easier to remove the fourth electron in the 3p sub-shell

Question 21

Why do melting points across periods not show a regular pattern?

Answer 21

Because melting points are directly linked to:
• the type of bonding between atoms of an element
• the structure of the element

Question 22

In period 3 why does silicon have the highest meltint point?

Answer 22

Because it has a giant covalent structure held together by strong covalent bonds

Question 23

Why do P, S, Cl and Ar have much lower melting points than the other elements of period 3?

Answer 23

Because they are only held together by van der waal forces