Learners' AlleyDesigned by Khow Willard

Atomic Structure

Set AAnswer key

From the lesson

9 marks

CThey have the same number of electrons.[1]

AChlorine-35 has 18 neutrons and chlorine-37 has 20 neutrons. BThe nucleon numbers are 35 and 37. DThe extra neutrons make chlorine-37 heavier.

D2.8.8.2[1]

AThe first shell holds only 2 electrons. BThe second shell is filled before the third shell, so 2.6.8.4 is in the wrong order. CThe third shell usually holds a maximum of 8 electrons.

Uranium-235: 92 protons, 143 neutrons (235 − 92) and 92 electrons[1]

Sodium ion: 11 protons, 12 neutrons and 10 electrons (11 − 1)[1]

Sulfide ion: 16 protons, 16 neutrons (32 − 16) and 18 electrons (16 + 2)[1]

(a)

5 protons, 6 neutrons (11 − 5) and 5 electrons[1]

(b)

2.3[1]

Phosphorus has the electronic configuration 2.8.5, so it also has 5 valence electrons.[1]

Elements with the same number of valence electrons have similar chemical properties.[1]

Practice

19 marks

Aproton in the nucleus, neutron in the nucleus, electron orbiting the nucleus[1]

Protons and neutrons are found in the nucleus of an atom while electrons are found in the electron shells around the nucleus.

BThe proton number of all atoms of an element is the same.[1]

AThe nucleon number is the number of protons plus the number of neutrons, so it is never less than the proton number. CAn atom of hydrogen-1 has no neutrons, so its nucleon number (1) equals its proton number (1). DA hydrogen-1 atom has 1 nucleon and 1 electron, so the two can be equal.

CK⁺, Ca²⁺, P³⁻[1]

AF⁻ has 10 electrons, Cl⁻ has 18 and Br⁻ has 36. BH⁺ has 0 electrons, He has 2 and N³⁻ has 10. CK⁺, Ca²⁺ and P³⁻ each have 18 electrons. DNa⁺ has 10 electrons, Mg²⁺ has 10 and S²⁻ has 18.

(a)

Isotopes are atoms of the same element with the same number of protons[1] but different numbers of neutrons.[1]

(b)

particle	number	name of particle
X	20	neutron
Y	18	electron
Z	17	proton

All three correct[2] (two correct earns 1 mark).

(c)

particle	number
X (neutrons)	18
Y (electrons)	17
Z (protons)	17

All three correct[2] (two correct earns 1 mark).

(a)

	relative mass	relative charge
proton	1	+1
neutron	1	0
electron	1/1836 or 1/1840	−1

Three blanks correct[1] and the other three blanks correct[1]

(b)(i)

27 − 13 = 14[1]

(ii)

2.8.3[1]

(iii)

They are isotopes. They are atoms of the same element with the same proton number (13) but different numbers of neutrons (14 and 13).[1]

(a)

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

(b)

isotope	protons	neutrons	electrons
²⁸⁶Fl	114	172	114
²⁸⁹Fl	114	175	114

Each correct row[1][1]

atom	protons	neutrons	electrons
³⁹₁₉K	19	20	19
⁵²₂₄Cr	24	28	24

Each correct row[1][1]

The atom is neutral, so protons = electrons = 24, which is chromium, and the nucleon number is 24 + 28 = 52.