Learners' AlleyDesigned by Khow Willard

Atomic Structure

Set BAnswer key

Multiple choice

6 marks

CThey have the same number of electrons.[1]

Mg²⁺, Ne, O²⁻ and Al³⁺ each have 10 electrons, arranged as 2.8.

AThey have different proton numbers, so they are different elements and not isotopes. BEach has 2 electron shells. DThe numbers of neutrons differ (for example 12 in magnesium-24 and 14 in aluminium-27).

D26[1]

X²⁺ has 2 fewer electrons than protons, so protons = 10 + 2 = 12. Nucleon number = 12 + 14 = 26.

C³⁷₁₇Z⁻[1]

The nucleon number is 17 + 20 = 37 and the proton number is 17. Only a negative ion fits the options with these numbers.

A, BThe nucleon number is 18, but it should be 37. DThe proton number is 18, but it should be 17.

D⁴⁰K⁺[1]

Chlorine-37 has 17 protons, 20 neutrons and 17 electrons. R has 19 protons (potassium), 21 neutrons and 18 electrons. The nucleon number is 19 + 21 = 40 and the charge is 19 − 18 = +1.

DS²⁻[1]

AAl³⁺ has 10 electrons: 2.8, so 2 shells. BBe²⁺ has 2 electrons: 2, so 1 shell. CN³⁻ has 10 electrons: 2.8, so 2 shells. DS²⁻ has 18 electrons: 2.8.8, so 3 shells.

Dproton number 20 and nucleon number 39[1]

X²⁺ has 18 electrons, so the atom has 18 + 2 = 20 electrons and 20 protons. Nucleon number = 20 + 19 = 39.

Structured questions

22 marks

(a)

A and E[1]

Both have more electrons than protons.

(b)

B and C[1]

Both have 17 protons but different numbers of neutrons (20 and 18).

(c)

17 + 20 = 37[1]

(d)

Sulfur (proton number 16)[1]

(e)

2− or −2[1]

It has 16 protons and 18 electrons.

(a)

Nucleon number 40 and electronic configuration 2.8.8[1]

(b)

R has a stable electronic configuration, with eight electrons in its valence shell (an octet), so it is unreactive.[1]

(c)(i)

Atoms of the same element with the same number of protons but different numbers of neutrons.[1]

(ii)

Isotopes of the same element have the same number of valence electrons.[1]

They have the same number of protons but different numbers of neutrons.[1]

Both have 92 protons.[1]

Uranium-235 has 143 neutrons (235 − 92) while uranium-238 has 146 neutrons (238 − 92).[1]

orSame proton number but different nucleon numbers.

(a)(i)

Deuterium ²₁H and tritium ³₁H (D and T are accepted as symbols)[1]

(ii)

Hydrogen, deuterium and tritium atoms each contain one proton.[1]

A deuterium atom has one more neutron than a hydrogen atom, while a tritium atom has two more neutrons than a hydrogen atom (use of data).[1]

(iii)

They all have one positively charged proton and one negatively charged electron, so they have equal numbers of positive and negative charges.[1]

(iv)

Heavy water has similar chemical properties to ordinary water, so it will not disrupt biological processes and can be used in the same way in the body.[1]

Deuterium atoms are twice as heavy as hydrogen atoms, so they can be detected using techniques such as mass spectrometry.[1]

(b)

name of ion	chemical symbol	number of electrons
hydrogen ion	H⁺	0
hydride ion	H⁻	2

Both correct[1]

Argon has the electronic configuration 2.8.8.[1]

It is unreactive because it has a fully filled valence shell.[1]

Calcium[1]

The proton numbers add up: 94 + 20 = 114.