Periodicity

Question 1

Describe how elements are arranged on the periodic table

Answer 1

By increasing atomic number.

Question 2

Describe the trends on the periodic table down a group

Answer 2

• Going down a group, elements contain the same number of outer electrons but an extra outer shell each time.
• A common number of electrons in the outer shell makes them have similar chemical properties

Question 3

Describe the trends on the periodic table across a period

Answer 3

Elements in the same row are arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from metallic to non-metallic characteristics.

Question 4

Which of the first 20 elements are metallic lattices?

Answer 4

• Li
• Be
• Na
• Mg
• Al
• K
• Ca

Question 5

What are metallic lattices?

Answer 5

Elements which experience metallic properties due to metallic bonding, such as conductivity, malleability and ductility.

Question 6

Which of the first 20 elements are covalent molecules?

Answer 6

• H2
• N2
• O2
• F2
• Cl2
• P4
• S8
• fullerenes (C60)

Question 7

What are covalent molecules?

Answer 7

Non-metal elements that do not conduct and have low melting and boiling points.

Question 8

Which of the first 20 elements are covalent networks?

Answer 8

• B
• C (diamond and graphite)
• Si

Question 9

What are covalent networks?

Answer 9

Elements which create a series of interlinking covalent bonds which produce high melting and boiling points.

Question 10

Which of the first 20 elements are monatomic?

Answer 10

Noble gases:
* He
* Ne
* Ar

Question 11

What is the screening effect?

Answer 11

When inner electron shells shield the outermost electrons from being effected by the attractive force of the increasing nuclear charge.

Question 12

Describe the term covalent radius

Answer 12

A measure of the size of an atom, half the
distance between the two nuclei in a covalent bond.

Question 13

Describe the trend of covalent radii across a period.

Answer 13

• As you move across a period, the covalent radius decreases as the nuclear charge of the atom increases with increasing protons.
• As the number of protons increases the nuclear charge increases which attracts the surrounding electrons and pulls in the energy levels closer to the centre. This decreases the atomic radius and hence the covalent radius.

Question 14

Describe the trend of covalent radii down a group.

Answer 14

• As you go down a group, the covalent radius increases as the number of energy levels an element has increases.
• If there are more energy shells the distance from the nucleus of the atom to the outer most energy shell increases.
• The screening effect occurs.
• This increases the atomic radius and hence the covalent radius.

Question 15

Describe the term ionisation energy

Answer 15

First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms.

Question 16

Describe the trend of ionisation energy across a period

Answer 16

• Across a period, the ionisation energy of an element increases as the electrons on the outermost electron shell are closer to the nucleus.
• The nuclear charge increases as the atomic number increases. Electrons have a higher attraction to the nucleus across a period and so require more energy to remove one mole of electrons.

Question 17

Describe the trend of ionisation energy down a group

Answer 17

• Down a group, the ionisation energy of an element decreases as there are more electron shells to shield the nuclear attraction to the electrons on the outer most shell.
• If there are more energy shells, the distance from the nucleus of the atom to the outer most energy shell increases.
• The screening effect occurs.
• Electrons on the outer most shell can be removed from the element easier.

Question 18

Describe the term electronegativity

Answer 18

Electronegativity is a measure of the attraction which an atom (involved in a bond) has for the electrons in the bond.

Question 19

Describe the trend of electronegativity across a period

Answer 19

• Electronegativity values increase across a period.
• This is due to the increasing electron affinity of the outermost electrons to the nucleus.
• The nuclear charge increases as the atomic number increases.
• Electrons have a higher attraction to the nucleus across a period so have a smaller covalent radius.
• This allows for bonding electrons to be more attracted to the nuclear charge of the other element and hence increases electronegativity.

Question 20

Describe the trend of electronegativity down a group

Answer 20

• Electronegativity values, in general, decrease down a group.
• This is due to the decreasing electron affinity of the outermost electrons to the nucleus.
• If there are more energy shells the distance from thenucleus of the atom to the outer most energy shell increases. This in turn increases the covalent radius.
• The screening effect occurs.
• Bonding electrons are therefore less attracted to the nuclear charge of the other atom.