Chemical Changes and Structures Flashcards Preview

Higher: Chemistry > Chemical Changes and Structures > Flashcards

Flashcards in Chemical Changes and Structures Deck (84):
1

The average rate of reaction is?

The change divided by the time

2

Relative rate of reaction is?

1/t

3

Particles have to collide with what for a collision to be succesful?

Enough EnergyCorrect Orientation

4

Collision Theory - Concentration

As concentration increases, there are more particles in the same volume. This means more collisions and thus more succesful collisions will occur. Rate will increase

5

Collision Theory - Surface Area

As surface area increases there are more  particles available to react. More collisions and therefore more succesful collisions will occur. Rate will increase

6

What is the Activation Energy?

The minimum kinetic energy required by colliding particles before a reaction may occur. The energy required to form an activated complex

7

Why does a catalyst increase rate of reaction?

Catalyst provides an alternative reaction pathway with a lower activation energy

8

What is temperature?

The measure of the average kinetic energy of all the particles of a substance

9

Temperature and reaction rate

When the temperature is increased there is an increase in the number of particles with energy higher than the activation energy

10

What is a potential energy diagram?

It can be used to show the energy pathway for a reaction. Shows the enthalpy change and the activation energy for both the forward and reverse reactions

11

What is the enthalpy change?

ΔH (kJ mol-1) The energy difference between products and reactants

12

Enthalpy change in exothermic reactions?

Negative value

13

Enthalpy change in endothermic reactions?

Positive value

14

What is the activated complex?

An unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction

15

Potential Energy Diagram - EA

Activation energy for the forward reaction when a catalyst is not present

16

Potential Energy Diagram - Ecat

Activation energy for the forward reaction when a catalyst is present

17

Potential Energy Diagram - ΔH

Enthalpy change for the forward reaction

18

Who created the Periodic Table?

The Russian scientist Dmitri Mendeleev 

19

How did Mendeleev create the Periodic Table?

He arranged elements in order of increasing atomic mass in conjunction with similar chemical properties, leaving gaps for elements that had not been discovered a that time

20

Groups 1 + 2 - Type of Bonding

Metallic

21

Groups 1 + 2 - Structure

Lattice 

22

Groups 1 + 2 - Melting Points

High

23

Groups 3 + 4 - Type of Bonding

Covalent

24

Groups 3 + 4 - Structure

Covalent Network

25

Groups 3 + 4 - Melting Point

High

26

Groups 5,6 + 7 - Type of Bonding

Covalent

27

Groups 5, 6 + 7 - Structure

Covalent Molecular 

28

Groups 5, 6 + 7 - Melting Points

Low

29

Group 0 - Type of Bonding

None

30

Group 0 - Structure 

Monatomic 

31

Group 0 - Melting Points

Low

32

What produces a metallic bond?

The electrostatic forces of attraction between the delocalised outer electrons and the lattice of positively charged ions

33

What holds the atoms of noble gases together?

Weak London dispersion forces

34

What forms a dipole?

The electrons in an atom or molecule being unevenly distributed 

35

What are London dispersion forces?

The weak forces of attraction between all atoms and molecules

36

Relative Strength of London Dispersion Forces

Much weaker than all other types of bonding

37

What causes London Dispersion Forces

Electrostatic attractions between temporary and induced dipoles caused by the movement of electrons in atoms and molecules

38

Effect of particle size on LDF strength

The larger the atoms or molecules the greater he number of electrons and the stronger the LDFs

39

What is a covalent bond?

The electrostatic attraction between positively charged nuclei and negatively charged electrons which are shared between the atoms involved 

40

Properties of Covalent molecular elements

Definite number of atoms bonded together in separate moleculesThey are discrete 

41

Properties of Covalent networks

Have a large but indefinite number of atoms bonded together

42

What is covalent radius?

Half of the distance between two atoms covalently bonded together. Measures the size of an atom

43

Covalent radius across a period

Decreases across a period due to increasing nuclear charge and no change in the number of occupied energy levels

44

Covalent radius down a group

Covalent radius increases down a group due to a greater number of occupied energy levels - outer electrons are further from the nucleus

45

Shielding effect

There is an increase in nuclear charge down a group however this is cancelled out by the shielding effect of the inner electrons 

46

What is the first ionisation energy?

The energy required to remove one mole of electrons from one mole of atoms in the gaseous state

47

First ionisation energy across a period

Increases because the distance between the outer electrons and the nucleus decreases due to the nuclear charge increasing. Also no change in shielding effect

48

First Ionisation energy down a group

Decreases because the atomic size increases and the complete inner electron energy levels shield the outer electrons from the attractive force of the nucleus

49

What is the second ionisation energy?

The energy required to remove one mole of electrons from one mole of one plus ions in the gas state

50

What is electronegativity?

A measure of the attraction an atom has for the shared electrons in a covalent bond

51

Electronegativity across a period

Increases due to increasing nuclear charge and decreasing atomic size.

52

Electronegativity down a group

Decreases due to an increase in atomic radius and increase in the number of energy levels, leading to a greater screening effect

53

The covalent bond is a result of?

Two positive nuclei being held together by their common attraction for the shared pair of electrons

54

When are polar covalent bonds formed?

When the attraction of each atom for the pair of bonding electrons is different. 

55

Polar Covalent Bonds: Differences in electronegativity 

The larger the difference in electronegativity between the two atoms the more polar the bond will be

56

Formation of ions

If the difference in electronegativity between the two atoms is greater than 1.8 then the movement of bonding from the element of lower electronegativity to the element of higher electronegativity is complete 

57

Bonding continuum 

Spectrum with pure covalent at one end and ionic at the other. Polar covalent bonding is in the middle

58

Compounds formed between metals and non-metals are?

Often, but not always, Ionic

59

Aqueous Acids are?

Ionic

60

Some metals can sometimes form?

Covalent bonds (e.g. SnI4)

61

All covalent molecules do what at a set temperature?

Boil and freeze

62

There are forces of attraction between covalent molecules called?

Intermolecular or Van Der Waals' forces

63

Intramolecular forces?

Hold atoms within a molecule 

64

Intermolecular forces are? 

Forces of attraction between molecules 

65

Any 'intermolecular' forces acting between molecules are known as?

Van der Waals' forces

66

Types of Van der Waals' forces

London Dispersion ForcesPermanent dipole: Permanent dipole interactionsHydrogen Bonds

67

London Dispersion Forces are?

Forces of attraction that can occur between all atoms and molecules formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by the movement of electrons in atoms and molecules

68

The strength of London Dispersion Forces is related to?

The number of electrons within an atom or molecule

69

A molecule is described as polar if?

It has a permanent dipole

70

The spatial arrangement of polar covalent bonds can result in?

A molecule having a permanent dipole, therefore being polar

71

Permanent dipole-Permanent dipole interactions are?

Additional electrostatic forces of attraction between polar molecules

72

Strength of dipole-dipole interactions 

Stronger than London Dispersion Forces with similar numbers of electrons 

73

The strongest dipole-dipole interaction is?

The hydrogen bond

74

The hydrogen bond is found when?

Hydrogen is bonded o a strongly electrostatic element such as nitrogen, oxygen or fluorine

75

Hydrogen bonds are?

Intermolecular forces of attraction between molecules which contain highly polar bonds 

76

Hydrogen Bond strength

Stronger than other forms of permanent dipole- permanent dipole interactions but weaker than a covalent bond 

77

Melting points, boiling points and viscosity can all be explained in terms of the type and strength of?

The intermolecular forces which exist between molecules

78

By considering the polarity and number of electrons present in molecules it is possible to?

Make qualitative predictions of the strength of the intermolecular forces

79

The melting and boiling points of polar substances are greater than?

The melting and boiling points of non-polar substances with similar numbers of electrons 

80

Melting points, boiling points, viscosity and solubility/miscibility in water are properties affected by?

Hydrogen bonding

81

The anomalous boiling points of ammonia, water and hydrogen fluoride are a result of?

Hydrogen Bonding

82

Hydrogen bonding in ice results in?

An expanded structure which causes the density of ice to be less than that of water at low temperatures 

83

Ionic compounds and polar molecular compounds tend to be soluble p in?

Polar solvents, such as water

84

Non-polar molecular substances tend to be soluble in?

Non-polar solvents, like heptane