Atomic Structure & the Periodic Table Exam Q Corrections

Gallium was discovered six years after Mendeleev published his periodic

table.

Give two reasons why the discovery of gallium helped Mendeleev’s

periodic table to become accepted.

(gallium) fitted in a gap (Mendeleev had left)

(gallium’s) properties were predicted correctly (by Mendeleev)

allow (gallium’s) pr

Which scientist first suggested that electrons orbit the nucleus at specific distances?

Bohr

The plum pudding model did not have a nucleus.

Describe three other differences between the nuclear model of the atom

and the plum pudding model.

any three from: (nuclear model)

• mostly empty space

allow the plum pudding model has no

empty space

allow the plum pudding model is solid

• the positive charge is (all) in the nucleus

allow in the plum pudding model the

atom is a ball of positive charge (with

embedded electrons)

do not accept reference to protons

• the mass is concentrated in the nucleus

allow in the plum pudding model the

mass is spread out

do not accept reference to neutrons

• the electrons and the nucleus are separate

allow in the plum pudding model the

electrons are embedded

allow in t

The model of the atom changed as new evidence was discovered.

The plum pudding model suggested that the atom was a ball of positive

charge with electrons embedded in it.

Evidence from the alpha particle scattering experiment led to a change in

the model of the atom from the plum pudding model.

Explain how.

most (alpha) particles passed (straight) through (the gold foil)

(so) the mass of the atom is concentrated in the nucleus / centre

or

(so) most of the atom is empty space

some (alpha) particles were deflected / reflected

(so) the atom has a (positively) charged nucleus / centre

if not awarded for MP2 allow (so) the

mass of the atom is concentrated in the nucleus / centre.

The radius of an atom of element X is 1.2 × 10−10 m

The radius of the centre of the atom is 1/10000 the radius of the atom.

Calculate the radius of the centre of an atom of element X.

Give your answer in standard form.

1.2 × 10−10 × 1 × 10−4

1

= 1.2 × 10−14 (m)

an answer of 1.2 × 10−14 (m) scores 2 marks

a correct answer

Chadwick’s experimental work on the atom led to a better understanding of

isotopes.

Explain how his work led to this understanding.

Chadwick provided the evidence to show the existence of neutrons

allow Chadwick discovered neutrons

(this was necessary because) isotopes have the same number of

protons

allow (this was necessary because)

isotopes have the same atomic number

or

element

(this was necessary because) isotopes are atoms of the same

ignore isotopes have the same number

of electrons

but with different numbers of neutrons

allow but with different mass (numbers)

The plum pudding model of the atom was replaced by the nuclear model.

The nuclear model was developed after the alpha particle scattering

experiment.

Compare the plum pudding model with the nuclear model of the atom.

In the periodic table, the transition elements and Group 1 elements are

metals.

Some of the properties of two transition elements and two Group 1 elements are shown in the table below. Use your own knowledge and the data in the table above to compare the

chemical and physical properties of transition elements and Group 1

elements.

Physical

Transition elements

• high melting points

• high densities

• strong

• hard

Group 1

• low melting points

• low densities

• soft

Chemical

Transition elements

• low reactivity / react slowly (with water or oxygen)

• used as catalysts

• ions with different charges

• coloured compounds

Group 1

• very reactive / react (quickly) with water / non-metals

• not used as catalysts

• white / colourless compounds

• only forms a +1 ion

What is the test for chlorine gas?

Damp litmus paper turns white

A student tested a metal chloride solution with sodium hydroxide solution.

A brown precipitate formed.

What was the metal ion in the metal chloride solution?

Iron(III)

The electronic structure of a neon atom shown in Figure 2 is not correct.

Explain what is wrong with the electronic structure shown in Figure 2.

(iii) protons and neutrons

do not allow electrons in nucleus

(relative charge of proton) +1

allow positive

(relative charge of neutron) 0

allow no charge/neutral

ignore number of particles

too many electrons in the first energy level or inner shell

allow inner shell can only have a maximum of 2

electrons

too few electrons in the second energy level or outer shell

allow neon has 8 electrons in its outer shell or neon

does not have 1 electron in its outer shell

allow neon has a stable arrangement of electrons

or a full outer shell

neon does not have 9 electrons or neon has 10 electrons

allow one electron missing

allow fluorine has 9 electrons

ignore second shell can hold (maximum) 8

electrons or 2,8,8 rule or is a noble gas or in Group

max 2 marks if the wrong particle, such as atoms

instead of electrons

if no other mark awarded allow 1 mark

Figure 2 shows what happens to the electrons in the outer shells

when a sodium atom reacts with a fluorine atom.

The dots (•) and crosses (×) represent electrons.

Use Figure 2 to help you answer this question.

Describe, as fully as you can, what happens when sodium reacts

with fluorine to produce sodium fluoride.

sodium (atom) loses

fluorine (atom) gains

one electron

ions formed

allow sodium forms positive (ion) or fluorine forms

negative (ion)

allow form ionic bond

allow to gain a full outer shell of electrons

allow forms noble gas structure

max 3 if reference to incorrect particle / bonding

Sodium fluoride is an ionic substance.

What are two properties of ionic substances?

Dissolve in water

High melting point