Periodicity

Question 1

How is nuclear charge of an atom given?

Answer 1

By the atomic number

Question 2

How is the effective nuclear charge experienced by the outer electrons less than the full nuclear charge?

Answer 2

Because the outer electrons are shielded from the nucleus because they are repelled by inner electrons- their presence reduces the attraction of the nucleus.

Question 3

Effective Charge definition and trend

Answer 3

• charge experienced by outer electrons, less than full nuclear charge
• increases across a period

Question 4

What is the atomic radius?

Answer 4

Half the distance between neighboring nuclei

Question 5

Atomic Radii Trends

Answer 5

• increase down a group because energy levels are added

- decrease across a period because electrons and protons are being added= more attraction, lessening the distance

Question 6

What is an ionic radius?

Answer 6

The radius of an atom’s ion

Question 7

Ionic Radius Trends

Answer 7

• positive ions are smaller than parent ions because they have lost electrons
• negative ions are larger than parent ions because they have gained electrons. Also there is electron repulsion, increasing the radii further
• ionic radius decrease from Group 1-14 for positive ions
• ionic radius decrease from Group 14-17 for negative ions
• ionic radius increases down a group with energy levels added
• decreases along period

Question 8

What is an ionization energy?

Answer 8

Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms

Question 9

Ionization Energies Trend

Answer 9

• increase across period. Stronger attraction between e+p= more energy needed to remove electrons
• decrease down a group. Less attraction between e+p because of shielding and far apart because more energy levels

Question 10

What is electron affinity?

Answer 10

Energy change when 1 mole of electron is added to 1 mole of gaseous atom

Question 11

Electron Affinity Trends

Answer 11

• Group 17 has high electron affinity, incomplete outer energy level, attract electrons the most
• Group 1 has low electron affinity- lack of protons and shielding within energy levels

Question 12

What is electronegativity?

Answer 12

• measure of the ability of atoms to attract electrons in a covalent bond

Question 13

Electronegativity Trends

Answer 13

• increase along a period as nuclear charge increases

- decreases down a group because of increase in energy levels

Question 14

Do metals or non-metals have lower ionization energies?

Answer 14

Metals have lower ionization energies than non-metals

- less energy needed to remove electrons from metals

Question 15

Melting Point Trends

Answer 15

• decrease down Group 1

- increase down Group 17

Question 16

Chemical Properties of Group 18

Answer 16

• noble gases
• monatomic- they exist as single atoms
• very unreactive- inability to lose or gain electrons
• very high ionization energies
• have a stable octet

Question 17

Chemical Properties Group 1

Answer 17

• alkaline metals
• good conductors of electricity
• more reactive as you travel down group
• form ionic compounds with non-metals

Question 18

Why is Group 1 good conductors of electricity?

Answer 18

because of the mobility of outer electron

Question 19

Group 1 Reaction with Water

Answer 19

• produces hydrogen and metal hydroxide

Question 20

What is lithium reaction with water

Answer 20

• floats, reacts slowly with water

- produces hydrogen but keeps shape

Question 21

What is sodium’s reaction with water

Answer 21

• vigorously reacts
• releases H+
• heat produced melts metal, forming small ball that moves around surface

Question 22

What is Potassium’s reaction with water

Answer 22

• vigorous reaction
• produce heat that ignites H+ into lilac coloured flame
• moves excitedly on water surface

Question 23

What are Group 1 Physical properties?

Answer 23

• good conductors of electricity and heat
• low densities
• grey shiny when freshly cut with knife