Ch7 Trends In The Periodic Table

Question 1

Heisenbergs uncertainty principle

Answer 1

Not possible to measure the distance between the nucleus and the outermost electrons of an atom

Question 2

Atomic radius

Answer 2

Of an atom is defined as half the distance between the nucleus and of two atoms of the Sam element that are joined together by a single covalent bond
Bond length

Question 3

How is atomic radius measured

Answer 3

X-ray diffraction and electron diffraction

Question 4

What is the covalent radius of a hydrogen molecule with distance between two nucleus = 0.074nm

Answer 4

0.037nm

Question 5

Why do noble gasses not have value for covalent radius

Answer 5

They don’t form covalent bonds with one another

Question 6

Atomic radius trend

Answer 6

Decrease across periods/rows
Increase down groups

Question 7

What is the size of an atom governed by

Answer 7

The electrostatic attraction between the positively charged protons and negatively charged electrons

Question 8

If electrostatic attraction between protons and electrons is large

Answer 8

the positive protons will pull the outer electrons closer to the nucleus giving a smaller atomic radius

Question 9

If electrostatic attraction is small

Answer 9

The electrons will be further from the nucleus giving a larger atomic radius

Question 10

Reasons: atomic radius increase down the groups

Answer 10

1. New energy level/ shells - additional electrons go into new energy levels as you go down. Outer electrons become further away from nucleus
2. Screening effect of inner electrons - electrons in inner energy levels shield/ screen outer electrons from positive charger of the nucleus giving a

Question 11

Reason: atomic radius decrease across a period

Answer 11

1. Increase in Effective Nuclear Charge - no. Of protons in nucleus increase from left to right in periodic table. Greater attractive force on outer electrons, draws them closer to nucleus
2. no increase in screening effect - extra electrons go into same outer shell as you go across

Question 12

First ionisation energy

Answer 12

Of an atom is the minimum energy required to completely remove the most loosely bound electrons of from a neutral gaseous atom in its ground state
Na(g) ->Na+(g) + e-

Question 13

First ionisation energy decrease down a group

Answer 13

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

Question 14

First ionisation increases across a period

Answer 14

1. Increasing effective nuclear charge
2. Decreasing atomic radius increase

Question 15

Exceptions to general trend across a period

Answer 15

-Higher than expected ionisation energies
- extra stability filled or half- filled sub levels
(Look to work copy)

Question 16

Second ionisation energy

Answer 16

Energy required to remove an electron from an ion with one positive charge in the gaseous state
X+(g) -> X2+(g) + e-

Question 17

Elevtronegeativity

Answer 17

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

Question 18

General points ionistaion energies

Answer 18

• steady increase as electrons removed, ion becomes more positive, greater attraction on remaining electrons

-large increase when electron removed from new energy level/ shells

-substantial increase when e removed from new sublevel

Question 19

Electro negativity trends

Answer 19

Decreases down a group
Increases across a period

Question 20

Electronegativity decrease down the groups

Answer 20

1. Increasing atomic radius
   -outer electrons are becoming further away from attractive force of nucleus
   -smaller attraction between nucleus and the shared pair of electrons … electroneg decreases
2. Screening effect of inner electrons
   -even though nuclear charge increases down groups, is cancelled out by the screening effect of intervening shells of electrons
   -outer electrons are shielded from attractive force of pos charged nucleus
   -attraction force of nucleus/ electronegativity decreases down groups

Question 21

Electronegativity increase across the periods

Answer 21

1. Increasing effective nuclear charge
   -moving left to right, number of protons in the nucleus increases, therefore attraction between nucleus and outer electrons is also increasing - electrons involved in binding are more strongly attracted to the nucleus
2. Decreasing atomic radius
   - within any row, the atomic radius decreases from left to right. Therefore outer electrons are closer to nucleus.
   Thus there is greater attraction between nucleus and the outer electrons

Question 22

Group 1

Answer 22

Alkali metals
Increasing reactivity down the group

Question 23

Group 1 points

Answer 23

-very reactive, low first ionisation values
-none occur free in nature, stored under oil or in glass container with air removed (Rb, Cs)
-low melting points
-readily lose single outer electron to form ionic compounds

Question 24

Group 1 chemical reactions with oxygen

Answer 24

Alkali metals react with oxygen to form oxides
Eg
Potassium + oxygen -> potassium oxide
2k + 1/2 O -> K2O

Question 25

Chemical reactions with water - group 1

Answer 25

Alkali metals react with water to form hydroxide of metal and hydrogen gas is given off Eg Sodium + water -> sodium hydroxide + hydrogen Na + H2O -> NaOH + 1/2H2

Question 26

Group 1 chemical reactions with acid

Answer 26

Too dangerous, explosive Sodium + hydrochloric acid -> sodium + hydrogen chloride Na + HCL -> NaCl + 1/2H

Question 27

Group 7

Answer 27

Halogens Increasing reactivity up the group

Question 28

Properties of halogens group 7

Answer 28

-most electronegative elements in table -fluorine most electronegative element, Electronegativity decreases down group -don’t exist free in nature -oxidising agents - removes electrons from other substances easily

Question 29

Trend in chemical reactivity of halogens 1 - chlorine + bromide

Answer 29

Chlorine gas bubbles through solution of bromide ions, chlorine takes electrons from bromide Chlorine displaces bromide from solution Chlorine + bromide —> chloride ion + bromine Cl2 + 2Br- —> 2Cl- + Br2

Question 30

Trend in chemical reactivity of halogens 2 - bromine + iodine

Answer 30

Bromine displaces iodine from solution Bromine + iodine ion —> bromide ions + iodine Br2 + 2I- —> 2Br- + I2 The more reactive halogens displaces the less reactive halogen from the solution of its ions

Question 31

Group 2

Answer 31

Alkaline earth metals

Question 32

Group 2 alkaline earth metals react with water and reason

Answer 32

Be does not Magnesium reacts very slowly Calcium undergoes steady reaction Reason: ionisation energies decrease down the group Strontium and barium react more vigorously with water to form

Question 33

Noble inert gases properties

Answer 33

Form practically no compounds, unreactive. -steady increase in boiling points down the group he - radon (Increasing atomic radius… more van der waals forces)

Question 34

Boiling points of halogens

Answer 34

Increase down the group -due to stronger van der waals forces as the atomic radius increases down the group

Question 35

Why do half full and full outer sub levels have higher ionisation energies

Answer 35

Extra stability, more difficult to remove electron and causes requires sudden increase in ionisation energy

Question 36

What happens. As you take away electrons

Answer 36

Atom becomes more positive and is holding into elect Ron’s more tightly -full outer sublevel more stable