Chemistry SAC

Question 1

Shapes of molecules are…

Answer 1

linear, bent, pyramidal and tetrahedral

Question 2

what is valence shell electron pair repulsion (VSEPR) theory

Answer 2

VSEPR theory states the electron pairs in the molecule repel each other and take up positions as far from one another as possible.

Question 3

what are polar bonds

Answer 3

Polar covalent bonds are covalent bonds in which the bonding electrons are unequally shared and, therefore, unsymmetrically distributed between the nuclei of two bonded atoms.

Question 4

what are non-polar bonds

Answer 4

are covalent bonds in which the bonding electron pair is shared equally

Question 5

Polar molecule is

Answer 5

-if they have a unsymmetrical shape their polar( bent/v-shaped and pyramidal.)

Question 6

Non-polar molecule is

Answer 6

Is a molecule that has a symmetrical shape (tetrahedral, (dipoles cancel out balance is created due to the pull being towards the middle) and linear )

Question 7

what is Intramolecular and Intermolecular and what they determine

Answer 7

Intramolecular bonding is the covalent bonds within molecules.
Intermolecular forces exist between molecules and hold molecules together. These forces are much weaker than covalent bonds, but they determine the temperature at which a molecular substance melts or boils, therefore, depends on the strength of the intermolecular forces. The stronger the intermolecular forces, the higher the melting or boiling point

Question 8

intermolecular forces(dispersion, dipole-dipole and H-bonding) properties and relation to shape

Answer 8

Dispersion forces(all gases) are effected number of electrons and shape ( tetrahedral= not strong force linear= strong force)
Dipole dipole
All polar molecules
Hydrogen bonds only operate between molecules when hydrogen is bonded to fluorine, oxygen or nitrogen.(FON)

Question 9

Physical properties of molecular substances (non-conduction of electricity) with reference to their structure

Answer 9

Molecular substances do not conduct electricity in the solid or molten form because the molecules are electrically neutral, and no delocalised electrons are present. Carbon, in the form of graphite, is an exception because it does have delocalised electrons and so conducts.

Question 10

what does the bond HF and HI have

Answer 10

HF:
shortest bond length=strongest bond length
(higher electronegativity difference=more pull+ stronger bond)
Has H-bonding=highest melting point
HI
greatest number of electrons=strong dispersion force

Question 11

Physical properties of molecular substances (including melting points and boiling points with reference to their structure

Answer 11

Molecular compounds have low melting and boiling points since the forces between the molecules are weak, and relatively little energy is required to break them. Many molecular substances are gases or liquids at room temperature.

Question 12

The structure and bonding of diamonds that explain its properties(including heat and electrical conductivity and hardness)

Answer 12

heat= good conductor of heat due to the strong covalent bonds
electrical conductivity= is not a good electrical conductor due to no free moving electrons.

hardness=very hard due to its big complex structure(strong directional bonding=covalent bonds everwhere) however also brittle= cut it the wrong way and it will shatter.

Question 13

The structure and bonding of graphite that explain its properties (including heat and electrical conductivity and hardness)

Answer 13

heat=Graphite is a good conductor of heat also due to its delocalised electrons. Energy can be easily transmitted= high melting point

electrical conductivity=Graphite is a good conductor of electricity because it contains charged particles that are free to move. These are the delocalised electrons.

hardness=Graphite is soft and feels slippery. due to the weak dispersion forces that the layers are help by.

chemically inert=Graphite is inert (it can withstand chemical change) due to its stable structure and delocalised electrons.

Question 14

The common properties of metals(lustre)

Answer 14

The lustrous appearance of a metal is due to the mobile electrons within the lattice being able to reflect light back into your eye, causing the metal to look shiny.

Question 15

The common properties of metals(malleability)

Answer 15

Metals are malleable and ductile, rather than brittle, as a result of the non-directional nature of metallic bonds.The attractive forces exerted by the cations for the mobile electrons occur in all directions. This means that layers of atoms can move past one another without disrupting the force between the cations and the negative sea of electrons.

Question 16

The common properties of metals(heat)

Answer 16

Metals are good conductors of heat. Electrons gain kinetic energy in hotter areas of the metal and quickly transfer it to other colder parts of the metal lattice due to the electron’s freedom of movement.

Question 17

The common properties of metals(electrical conductivity)

Answer 17

Metals are good conductors of electricity. When an electric field is applied to a metal, one end of the metal becomes positive and the other becomes negative. also good conductors of electricity= due to the delocalised/ free moving electrons present.

Question 18

Crystal nature of metallic bonding

Answer 18

have low electronegativities, which means they tend to lose their outer shell electrons easily. Once a metallic atom has lost its outer shell electron, it becomes a cation (positively charged)

Question 19

what is Electrostatic forces

Answer 19

Electrostatic forces of attraction between the cations and the negatively charged valence electrons

Question 20

The common properties of ionic compounds (brittleness, hardness)

Answer 20

Hardness-Ionic compounds are hard=The surface of the crystal is not easily scratched due to the strong ionic bond holding the ions together
brittle (not malleable or ductile)=Distortion of the crystal causes ions of like charge to come close together and the repulsion between these ions breaks or shatters the crystal

Question 21

The common properties of ionic compounds (melting point)

Answer 21

Melting point-Ionic compounds have high melting and boiling points =A large amount of energy is needed to separate the ions

Question 22

The common properties of ionic compounds (difference in electrical conductivity in solid and molten liquid states)

Answer 22

Electrical conductivity-Ionic compounds will not conduct electricity in the solid form=The charged particles (ions) are not able to move
Will conduct electricity when molten (or melted) =In the molten solution, oppositely charged ions are able to slide past one another and will therefore be able to conduct electricity
Will conduct electricity in an aqueous solution (dissolved in water).=When an ionic substance is dissolved in water, the ions dissociate from the lattice and can move freely to conduct an electric current. The solution is called an electrolyte

Question 23

The common properties of ionic compounds (lustre)

Answer 23

lustre-Ionic compounds do not have lustre or are not shiny=There are no free electrons moving in the structure to reflect light as they are involved in the strong electrostatic ionic bonds (unlike metals!)

Question 24

formation of ionic compounds

Answer 24

metal atoms donate one or more electrons to non-metal this is called electron transfer. non metal gain metal lose

Question 25

The nature of ionic bonding

Answer 25

This transfer of electrons results in ion formation:
sodium atoms lose an electron and become positively charged sodium ions (cations)
chlorine atoms gain an electron and become negatively charged chloride ions (anion).
These oppositely charged ions attract each other by electrostatic attraction. This strong force of attraction between positive and negative ions is what produces an ionic bond.

Question 26

writing of ionic compound formulas, including those containing polyatomic ions and transition metal ions

Answer 26

polyatomic ions=charged ion composed of two or more atoms
transition metal ions=Iron, for example, can form black FeO and brown Fe2O3, each with different physical and chemical properties.iron(II) and (III), copper(I) and (II), and mercury(I) and (II)

Question 27

What is electrolyte

Answer 27

Solution or liquid that can conduct electricity

Question 28

Why do ionic bonds conduct electricity in liquid and molten form

Answer 28

Because they can move freely in those states