Chapter 7 - Trends in the Periodic Table

Question 1

Atomic radius (covalent radius)

Answer 1

Half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond

Question 2

Bond length

Answer 2

Distance between the nuclei of two atoms

Question 3

Van der Waals radius

Answer 3

Distance between atoms that are just touching; unsquashed like noble gases which don’t form bonds

Question 4

Values of atomic radius ______ down the groups in the Periodic table because…

Answer 4

Values of atomic radius increases down the groups in the Periodic table because:

1. New shell/energy level is being filled
2. Screening effect of inner electrons

Question 5

Values of atomic radius ______ across a period in the Periodic table because…

Answer 5

Values of atomic radius decrease across a period in the Periodic table because:

1. Increase in effective nuclear charge
2. No increase in the screening effect

Question 6

Effective nuclear charge

Answer 6

Effective pull of the nucleus on electrons

Question 7

Which are bigger than the atom they came from: positive or negative ions?

Answer 7

Negative ions are larger than the atom they came ffrom beacause there are more electrons to old on to. Similary, positive ions are smaller because they may have lost a layer of electrons and there is now a greater number of protons than electrons

Question 8

Why do values of atomic radius generally stay the same across the transition elements?

Answer 8

The pull of the increasing number of electrons is offset by the extra screening due to the increasing number of 3d electron

Question 9

First ionisation energy

Answer 9

Minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state

Question 10

What is ionisation energy measured in?

Answer 10

kilojoules per mole

kJ mol¯¹

Question 11

Ionisation energy

Answer 11

Measure of the energy needed to pull a particular electron away from the attraction of the nucleus

Question 12

What governs the size of the attraction between electrons and the nucleus?

Answer 12

○Charge on the nucleus

○Distance of the electrons from the nucleus

Question 13

Values of first ionisation energy ______ down groups in the Periodic Table because:

Answer 13

Values of first ionisation energy decrease down groups in the Periodic Table because

1. Increasing atomic radius
2. Screening effect of inner electrons

Question 14

Values of first ionisation energy ______ across a period in the Periodic Table because:

Answer 14

Values of first ionisation energy increase across a period in the Periodic Table because:

1. Increasing effective nuclear charge
2. Decreasing atomic radius

Question 15

Why are Be & N and Mg & P exceptions to the trends in first ionisation energy?

Answer 15

They have higher first ionisation values than expected due to the fact that any sublevel that is completely filled (e.g. beryllium or magnesium) or exactly half filled (e.g. nitrogen or phosphorus) has extra stability, and therefore more energy is required to break these stable arrangements

Question 16

Second ionisation energy

Answer 16

Energy required to remove an electron from an ion with one positive charge in the gaseous state

Question 17

Why do successive ionisation energies increase?

Answer 17

Once you have removed the first electron, you are left with a positive ion. Trying to remove a negative electron from a positive ion is going to be more difficult than removing it from an ion

Question 18

Electronegativity

Answer 18

Relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Question 19

What is the most electronegative element?

Answer 19

Fluorine

Question 20

Values of electronegativity ______ down groups in the Periodic Table because:

Answer 20

Values of electronegativity decrease down groups in the Periodic Table because:

1. Increasing atomic radius
2. Screening effect

Question 21

Values of electronegativity ______ across periods in the Periodic Table because:

Answer 21

Values of electronegativity increase across periods in the Periodic Table because:

1. Increasing effective nuclear charge
2. Decreasing atomic radius

Question 22

What are the properties of alkali metals?

Answer 22

○Very reactive
○Don’t occur free in nature
○Low first ionisation energies and low electronegativity →readily form ionic compounds by losing their single outer electron
○Reactivity increases down the group
○Reaction with oxygen forms oxides
○Reaction with water forms hydroxides
○Reaction with dilute acids is very dangerous as so much hydrogen is released in a short time that explosions can occur

Question 23

What are the properties of halogens?

Answer 23

○Most electronegative element
○Quite reactive
○Don't exist free in nature
○Reactivity increases up the group
○Any element higher in the group will displace the less reactive halogen from the solution of its ions

Question 24

What are the properties of Noble gases?

Answer 24

○As you go down the group, boiling point increases as atomic radius decreases