Atomic Structure

Question 1

Briefly describe the structure of an atom

Answer 1

The atom is mainly empty space with the mass of the atom concentrated in the nucleus which is small and dense. The electrons orbit the nucleus in electron shells

Question 2

Relative masses of protons, electrons and neutrons

Answer 2

P- 1
E- 1/1837
N- 1

Question 3

Relative charges of protons, electrons and neutrons

Answer 3

P- +1
E- -1
N- 0

Question 4

Define isotope

Answer 4

Atoms of the same element having the same number of protons but different number of neutrons

Question 5

Why do isotopes of the same element have the same chemical properties?

Answer 5

Different isotopes of the same element will have the same chemical reactivity as they have the same number of electrons hence the same electronic configuration

Question 6

Why do isotopes of the same element have different physical properties?

Answer 6

The mass and density of isotopes are different

Question 7

Define relative atomic mass

Answer 7

Weighted average mass of the different isotopes of an element as compared to 1/12th the mass of a C-12

Question 8

Define the unified atomic mass unit

Answer 8

Weighted average mass of an atom of an element as compared to 1/12th the mass of a C-12 atom

Question 9

What are the main energy levels known as?

Answer 9

Principal quantum number (n) (shell number)

Question 10

What is the principal quantum levels divided into?

Answer 10

They are divided into subshells

Question 11

What are subshells denoted by?

Answer 11

s,p,d,f

Question 12

Define orbitals

Answer 12

Each subshell is made of orbitals. An orbital is a region around the nucleus where there is the greatest probability of locating a particular electron

Question 13

What is the maximum number of electrons an orbital may contain?

Answer 13

2

Question 14

What are the subshells and the number of electrons they may contain?

Answer 14

s - 2
p - 6
d - 10

Question 15

What does the groundstate e.c of an atom mean?

Answer 15

The e.c of an uncharged atom

Question 16

Why do we fill the 4s orbital before the 3d orbital?

Answer 16

In terms of energy, the 4s orbital has lower energy than the 3d orbital

Question 17

What is the shape of a s orbital?

Answer 17

Spherical shape

Question 18

What is the shape of a p orbital?

Answer 18

Dumbell shape

Question 19

Define first ionisation energy

Answer 19

Amount of energy to remove one mole of electrons from one mole of gaseous atoms to produce one mole of unipositive gaseous ions

Question 20

General equation for first ionisation energy

Answer 20

X(g) ——-> X+(g) + e-

Question 21

Define second ionisation energy

Answer 21

Amount of energy required to remove one mole of electrons from one mole of unipositive gaseous ions to produce one mole of dipositive gaseous ions

Question 22

General equation for second ionisation energy

Answer 22

X+(g) ——> X2+(g) + e-

Question 23

State and explain what is the general trend in first ionisation energy across a period

Answer 23

First ionisation energy increases across a period (becomes harder to remove the e-). The number of electrons increases but the shielding effect does not increase as the number of shells does not increase (electrons added are in the same shell) and number of protons increase thus effective nuclear charge increases. Electron - nuclear attraction increases

Question 24

State and explain what happens to first ionisation energy down the group

Answer 24

First ionisation decreases down the group. Down the group the shielding effect increases due to additional shells of electrons. Electron-nuclear attraction decreases and nuclear charge decreases. Becomes easier to remove ionising electrons

Question 25

Factors affecting ionisation energy (3)

Answer 25

Nuclear charge
Shielding effect
Atomic radius (electron-nuclear attraction)

Question 26

Define nuclear charge

Answer 26

The greater the number of protons in the nucleus of an atom, the greater will be the force of attraction of electrons

Question 27

Define shielding effect

Answer 27

The inner electrons shield the valence electrons from the full attractive forces of the protons in the nucleus

Question 28

What does a big jump in ionisation energies indicate?

Answer 28

A change of shells

Question 29

Explain why there is a slight decrease in first ionisation energy between elements of group 2 and 3 (e.g. Mg and Al)

Answer 29

The electron to be removed from aluminium is found in the 3p subshell which experiences additional shielding from the 3s electron. Hence the electron nuclear attraction of aluminium is lower than that of magnesium

Question 30

Explain why there is a slight drop in first ionisation energy between elements of group 15 to 16 (e.g. P and S)

Answer 30

The electron to be removed from group 16 will experience spin pair repulsion and ionising electron is easier to remove

Question 31

What are ionisation energies due to?

Answer 31

They are due to the attraction between nucleus and valence electrons