3.1.3 Bonding

Question 1

describe an ionic bond

Answer 1

• Ionic bonding occurs between metals and non-metals * electrons are transferred from metal atoms to non-metal atoms * positive and negative ions are formed

Question 2

when is a positive or a negative ion formed?

Answer 2

Positive ions are formed when an atom loses one or more electrons and a negative ion is formed when an atom gains one or more electrons

Question 3

what sort of attraction does an ionic bond have?

Answer 3

ionic bonding is the result of electrostatic attraction between oppositely charged ions. The attraction extends throughout the compound. Every positive ion attracts every negative ion and vice versa. Ionic compounds always exist in a structure called a lattice.

Question 4

properties of ionically bonded compound’s structure in room temperature

Answer 4

• solid at room temperature because of high melting temperatures, as it is arranged in a lattice, and strong attractions between ions.

Question 5

current in metals and in ionic compounds

Answer 5

A current of electricity is a flow of charge. In metals, negative electrons move. In ionic compounds, charged ions move.

Question 6

What is a small group of covalently bonded atoms called?

Answer 6

A molecule

Question 7

What is covalent bonding?

Answer 7

when non-metals share electrons to get a noble gas arrangement.

Question 8

How is one pair of covalent bonding represented? How is two pairs of covalent bonding represented?

Answer 8

by a line, e.g. Cl-Cl by a double line, e.g. O=O

Question 9

how does sharing electrons hold atoms together?

Answer 9

Atoms with covalent bonds are held together by the electrostatic attraction between the nuclei and the shared electrons. This takes place within the molecule. e.g. hydrogen molecule consists of 2 protons held together by a pair of electrons. The repulsive forces and the attraction forces balance when the nuclei are a particular distance apart.

Question 10

properties of substances with molecular structure

Answer 10

Substances composed of molecules are gases, liquids, or solids with low melting temperatures. This is because the strong covalent bonds are only between the atoms within the molecules.

Question 11

What is coordinate bonding, (dative covalent bonding)?

Answer 11

Coordinate (dative covalent) bond contains a shared pairs of electrons with both electron supplied by one atom. When a coordinate bond forms, a lone pair of electrons become a bonding pair of electrons. Once formed, the co-ordinate bond is identical to a normal covalent bond.

Question 12

Explain the formation of ammonium ion

Answer 12

Ammonia, NH3, has a lone pair of electrons. In the Ammonium ion, NH4+, the nitrogen uses its lone pair of electrons to form a coordinate bond with a H+ ion (a bare proton with no electrons at all and therefore electron-deficient)

Question 13

How is coordinate bond represented?

Answer 13

by an arrow ->

Question 14

What is a metallic bond?

Answer 14

A metallic bond is the attraction between delocalised electrons and positive ions arranged in a lattice. Delocalised electrons are those that are not confined to any one atom and can move throughout the lattice.

Question 15

Properties of metals

Answer 15

Metals are good conductors of electricity and heat. (Sea of electrons are responsible for this).

Question 16

What is electronegativity?

Answer 16

It is the power of an atom to attract the electron density in a covalent bond towards itself.

Question 17

What term is used to describe the way the negative charge is distributed in a molecule?

Answer 17

electron density

Question 18

What is the Pauling Scale?

Answer 18

It is used as a measure of electronegativity. It runs from 0 to 4. The greater the number, the more electronegative the atom. The noble gases have no number because they do not, in general, form covalent bonds.

Question 19

what are the three factors that electronegativity depends on?

Answer 19

1) the nuclear charge 2) the distance between the nucleus and the outer shell electrons 3) the shielding of the nuclear charge by electrons in the inner shells.

Question 20

Effects of a smaller atom and a larger nuclear charge (for a given shielding effect) on electronegativity

Answer 20

• the smaller the atom, the closer the nucleus is to the shared outer main level electrons and the greater its electronegativity. • the larger the nuclear charge (for a given shielding effect), the greater the electronegativity.

Question 21

Trends in electronegativity across a period

Answer 21

Going across a period in the periodic table, the electronegativity increases. The nuclear charge increases, the number of in a main levels remain the same and the atoms become smaller.

Question 22

Trends in electronegativity going up a group

Answer 22

Going up a group in the periodic table, electronegativity increases (the atoms get smaller) and there is less shielding by electrons in inner shells.

Question 23

where are the most electronegative atom is found in the periodic table?

Answer 23

The most electronegative atom is a found at the top right hand corner of the periodic table (ignoring the noble gases which form few compounds). The most electronegative atom is a fluorine, oxygen and nitrogen followed chlorine.

Question 24

Polarity in covalent bonds between two atoms that are the same

Answer 24

When both atoms are the same, e.g. in fluorine, F2, the electrons in the bond must be shared equally between the atoms. Both atoms have exactly the same electronegativity and the bond is completely non-polar.

Question 25

Polarity in covalent bonds between two atoms that are different

Answer 25

In a covalent bond between two atoms that have a small difference in electronegativity, the electron pair is not shared equally but is displaced more towards the more electronegative atom, forming a polar covalent on.

Question 26

how is the asymmetrical distribution of electrons represented?

Answer 26

By the use of partial charges δ+ (delta plus) and δ- (delta minus), above the atoms in the bond. The δ- is placed above the atom that has the higher electronegativity value and the δ+ is placed above the atom with the lower electronegativity value.

Question 27

How is a dipole caused?

Answer 27

The difference in charge between the two atoms, caused by a shift in electron density in the bond, is called a dipole.

Question 28

Polarity of molecules

Answer 28

Simple covalent molecules can be polar or non-polar. The polarity depends on the presence of polar bonds, and also on their shape. If a molecules contains equally polar bonds arranged symmetrically, then the polarities of the bond cancel each other out and the molecule is non-polar, for example, CO2, is a linear molecule.

Question 29

name the 3 types of intermolecular forces

Answer 29

• Van der Waals forces - acts between all atoms and molecules (weakest) *Dipole-dipole forces - acts only between certain types of molecules (medium strength) *Hydrogen bonding - acts only between certain types of molecules. (strongest)

Question 30

What’s dipole-dipole forces?

Answer 30

Dipole-dipole forces act between molecules that permanent dipoles. E.g. in the hydrogen chloride molecule, chlorine is more electronegative then hydrogen. So the electrons are pulled towards the chlorine atom rather than the hydrogen atom. The molecule therefore has a dipole and is written H^δ+ - Cl^δ-. Two molecules which both have dipoles will attract one another. Whatever their starting positions, the molecules with dipoles will ‘flip’ to give an arrangement where the two molecules attract.

Question 31

What’s Van der Waals forces?

Answer 31

Electrons are always moving in an atom, and this causes an unequal distribution of electrons, resulting in a temporary induced dipole. But van der Waals forces (induced dipole-dipole forces) are attractions between these induced dipoles.

Question 32

What affect does more electrons have in the van der Waals forces?

Answer 32

More electrons=greater the van der Waals forces of attraction between molecules - explaining increase in boiling points of alkanes as the chain increases in length, and in increase in boiling point down group 7.

Question 33

What is hydrogen bonding?

Answer 33

Hydrogen bonds are permanent dipole-dipole attractions between a δ+ H atom (that is covalently bonded to very electronegative atoms - O, N, or F) in one molecule and a δ- O, N or F atom in another molecule. The hydrogen bond is formed because of attraction between a lone pair of electrons on the δ- atom and the δ+ hydrogen atom.

Question 34

What is intermolecular forces? and what is intramolecular forces? what is broken when heated?

Answer 34

Intermolecular forces are between the molecules - these are broken when heated or melted. Intramolecular forces are within the molecules - e.g. covalent bonds.

Question 35

How is hydrogen bond used when water becomes ice?

Answer 35

When water freezes, the water molecules are no longer free to move about and hydrogen bonds hold the molecules in fixed positions. The resulting three-dimensional structure, resembles the structure of diamond.

Question 36

How does the structure of ice affect its density

Answer 36

In order to fit into the ice structure, the molecules are slightly less closely packed then in liquid water. This means that ice is less dense than water and forms on top of prawns rather than at the bottom.

Question 37

What is the electron pair repulsion theory?

Answer 37

Each pair of electrons around an atom will repel all electron pairs. The pairs of electron will therefore take up position as far apart as possible to minimise repulsion.

Question 38

Shapes of molecules with 2 pairs of electrons and give an example.

Answer 38

linear - 180º apart, Beryllium chloride (BeCl2)

Question 39

Shapes of molecules with 3 pairs of electrons and give an example

Answer 39

trigonal planar - 120º apart, Boron trifluoride (BF3)

Question 40

Shapes of molecules with 4 pairs of electrons and give an example

Answer 40

tetrahedron - 109.5º apart, Methane (CH4) and Ammonium ion (NH4+)

Question 41

Shapes of molecules with 5 pairs of electrons and give an example

Answer 41

trigonal bipyramid - 120º and 90º apart, phosphorus pentachloride (PCl5)

Question 42

Shapes of molecules with 6 pairs of electrons and give an example

Answer 42

octahedral - 90º apart, sulfur hexafluoride (SF6)

Question 43

properties of ionically bonded compound’s electricity

Answer 43

• conduct electricity when molten or dissolved in water (aqueous) but not when solid. This is because the ions carry the current are free to move in the liquid state but not free in the solid-state.

Question 44

properties of ionically bonded compound’s strength

Answer 44

• brittle and shatter easily when given a blow. This is because they form a lattice of alternating positive and negative ions. A blow may move the ions and produce contact between ions with like charges, causing them to repel from one another.

Question 45

properties of substances with molecular structure (attraction between molecules)

Answer 45

There is only a week attraction between the molecules so the molecules do not need much energy to move apart from each other.

Question 46

properties of substances with molecular structure (conduction)

Answer 46

They are poor conductors of electricity because the molecules are neutral overall. This means that there is no charged particles to carry the current. If they dissolve in water, and remain as molecules, the solutions do not conduct electricity. Again, this is because there are no charged particles.

Question 47

Properties of metallic bonding (strength)

Answer 47

Strength of metallic bond increases if the ionic charge increases

Question 48

properties of metallic bonding (temperature of melting/boiling points)

Answer 48

Metals have high melting points because they have giant structures.

Question 49

Size of metallic bond to the strength of the bond

Answer 49

The smaller the size of the ion the closer the electrons are to the positive nucleus and the stronger the bond.

Question 50

Shape of metallic bonds

Answer 50

Metals are malleable and ductile (can be pulled into thin wires).

Question 51

effect of ice density of ice on a pond

Answer 51

This insulates the pond and enable fish to survive through the winter; (must have helped life to continue, in the relative warmth of the water under the ice, during the ice age.

Question 52

What do dotted lines represent in 3D representations of molecules?

Answer 52

bond going towards the paper, away from the reader.

Question 53

What do wedges represent in 3D representations of molecules?

Answer 53

bond coming out of the paper

Question 54

Shape of Ammonia

Answer 54

triangular pyramid with one lone pair

Question 55

Explain how lone pair repulsion affect the shape of Ammonia?

Answer 55

bonding pairs of electrons attracted towards Nitrogen nucleus, and hydrogen nucleus. Lone pair is only attracted by nitrogen nucleus and is pulled closer to it than shared pairs. Greater repulsion between lone pairs and shared pairs - squeezing hydrogen atoms together.

Question 56

Shape of water

Answer 56

bent shape (2 shared bonds and 2 lone pairs)

Question 57

shape of chlorine tetrafluoride ion, ClF4-

Answer 57

4 bonds and 2 lone pairs - square planar

Question 58

order of repulsion strength (weakest to strongest), between bonding pairs and lone pairs.

Answer 58

1) bonding pair - bonding pair,
2) lone pair - lone pair,
3) lone pair - lone pair.

Question 59

Shape, angles of molecules we 2 bonding pairs and 2 lone pairs, include an example

Answer 59

Bent, 104.5• H2O

Question 60

Shape, angles of molecules with 3 bonding pairs and 1 line pair, include an example

Answer 60

Trifocals planar, 107• NH3

Question 61

Shape, angles of molecules we 2 bonding pairs and 2 lone pairs, include an example

Answer 61

Bent, 104.5• H2O

Question 62

Shape, angles of molecules with 3 bonding pairs and 1 line pair, include an example

Answer 62

Trifocals planar, 107• NH3