Question
This question is about the first 30 elements in the Periodic Table.
Name the element which:
(a) is 78% of clean, dry air [1]
(b) has atoms with an electronic structure of 2,8,1 [1]
(c) is extracted from hematite [1]
(d) forms an oxide with a giant covalent structure [1]
(e) is the gas with the slowest rate of diffusion at room temperature[1]
(f) has an anhydrous chloride which turns pink when water is added[1]
(g) has aqueous ions which form a white precipitate when added to aqueous silver ions[1]
(h) forms a blue hydroxide which dissolves in aqueous ammonia[1]
(i) is added to molten iron to remove impurities in the steel making process[1]
(j) is used to galvanize iron. [1] [Total: 10]
Answer/Explanation
Ans:
1(a) nitrogen
1(b) sodium
1(c) iron
1(d) silicon
1(e) chlorine
1(f) cobalt
1(g) chlorine
1(h) copper
1(i) oxygen
1(j) zinc
Question
The Periodic Table is a method of classifying elements.
(a) Identify the element which is in Group VI and Period 4.
(b) Calcium is in Group II and chlorine is in Group VII of the Periodic Table.
Explain, in terms of number of outer shell electrons and electron transfer, how calcium atoms
and chlorine atoms form ions. Give the formulae of the ions formed.
(c) Group V chlorides are covalent molecules. The boiling points of some Group V chlorides are
shown.
(i) Suggest the approximate boiling point of \(PCl_3\).
(ii) Explain the trend in boiling points in terms of attractive forces between particles.
(iii) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of
\(PCl_3\).
Show outer electrons only.
(d) PCl 3 reacts with chlorine, Cl2, to form PCl 5. This reaction is exothermic and reaches an
equilibrium.
\(PCl_3(g) + Cl_2(g) \leftrightarrow PCl_5(g)\)
(i) Describe two features of an equilibrium.
(ii) State the effect, if any, on the position of this equilibrium when the following changes are
made.
Explain your answers.
temperature is increased ……………………………………………………………………………………….
pressure is increased ……………………………………………………………………………………………
(iii) Explain, in terms of particles, what happens to the rate of the forward reaction when the
reaction mixture is heated.
(e) \(PCl_5\) reacts with lithium fluoride, LiF, to form \(LiPF_6\).
\(PCl_5 + 6LiF → LiPF_6 + 5LiCl\)
Calculate the mass of LiF needed to form 3.04g of \(LiPF_6\) using the following steps.
● Calculate the number of moles of LiPF6 formed.
[Mr : \(LiPF_6\), 152]
number of moles = …………………………
● Deduce the number of moles of LiF needed.
number of moles = …………………………
● Calculate the mass of LiF needed.
mass = ………………………… g
(f) Lithium fluoride has ionic bonding.
(i) What is an ionic bond?
(ii) Give two physical properties of ionic compounds.
Answer/Explanation
Answer:
(a) selenium / Se
(b) Ca has 2 and Cl has outer electrons 7 (1)
Ca (atoms) lose electrons (1)
Cl (atoms) gain electrons (1)
\(Ca^{2+}\) (ions) (1)
\(Cl^–\) (ions) (1)
(c) (i) any number in the range 72 – 129°C
(ii) 3 P- Cl dot cross bonds (1)
2 (only) non-bonding electrons to make an octet on P (1)
6 (only) non-bonding electrons to make an octet on each Cl (1)
(d) (i)
constant concentrations (1)
rate of forward reaction
= rate of reverse reaction (1)
(ii) increased temperature:
(equilibrium) shifts to LHS (1)
(forward) reaction is exothermic (1)
increased pressure:
(equilibrium) shifts to RHS (1)
fewer moles (of gas) on RHS (1)
(iii) rate increases and particles have more energy (1)
more collisions (between particles) occur per second / per unit time
more (of the) particles / collisions have energy greater than activation energy
or
more (of the) particles / collisions have sufficient energy to react
or
a greater percentage / proportion / fraction of collisions (of particles) are successful
(e) mol of LiPF6 = 3.04 / 152 = 0.02(00) (1)
mol of LiF = 0.02(00) × 6 = 0.12(0) (1)
mass of LiF = 3.12 g (1)
(f) (i) oppositely charged ions
(ions) are attracted
(ii) any two from:
physical constants: high boiling point / melting point
conductivity: conduct (electricity) when aqueous or conduct (electricity) when molten
solubility: soluble in water
Question
This question is about elements $\mathbf{X}, \mathbf{Y}$ and $\mathbf{Z}$.
(a) An atom of element $\mathbf{X}$ is represented as ${ }_{16}^{34} \mathbf{X}$.
(i) Name the different types of particles found in the nucleus of this atom of $\mathbf{X}$.[2]
(ii) What is the term for the total number of particles in the nucleus of an atom?[1]
(iii) What is the total number of particles in the nucleus of an atom of ${ }_{16}^{34} \mathrm{X}$ ?[1]
(iv) What is the electronic structure of the ion $\mathbf{X}^{2-}$ ?[1]
(v) Suggest the formula of the compound formed between aluminium and $\mathbf{X}$.[1]
(b) (i) What term is used to describe atoms of the same element with different numbers of particles in the nucleus?
(ii) Identify the atom against which the relative masses of all other atoms are compared.[1]
(iii) What is the name of the amount of any substance that contains $6.02 \times 10^{23}$ particles?[1]
(iv) The constant $6.02 \times 10^{23}$ has a name.
What is the name of this constant?[1]
(c) Part of the definition of relative atomic mass is ‘the average mass of naturally occurring atoms of an element’.
Some relative atomic masses are not whole numbers.
Element $\mathbf{Y}$ has only two different types of atom, ${ }^{69} \mathbf{Y}$ and ${ }^{71} \mathbf{Y}$.
The ratio of atoms present in element $\mathbf{Y}$ is shown.
$
{ }^{69} \mathbf{Y}:{ }^{71} \mathbf{Y}=3: 2
$
- Calculate the relative atomic mass of element $Y$ to one decimal place.
relative atomic mass = …………………………
● Identify element Y.
(d) Element Z is in Period 3 and Group V.
(i) Identify element Z………………………………………………………………………………………………………………………. [1]
(ii) Explain in terms of electron transfer why Z behaves chemically as a non-metal………………………………………………………………………………………………………………………. [2] [Total: 16]
▶️Answer/Explanation
Ans:
1(a)(i) protons 1
neutrons 1
1(a)(ii) nucleon number
1(a)(iii) 34
1(a)(iv) 2 : 8 : 8
$1(a)(v) \quad A b_2 X_3$
1(b)(i) isotopes
1(b)(ii) $\quad{ }^{12} \mathrm{C}$
1(b)(iii) a mole
1(b)(iv)
Avogadro constant
1(c) $
M 1(3 \times 69)+(2 \times 71)
$
$
M 2=\frac{349}{5}=69.8
$
$\mathrm{M} 3 \mathrm{Y}=\mathrm{Ga} /$ gallium
1(d)(i) phosphorus / P 1
1(d)(ii) gains electrons
three electrons (when forming ion)