Topic 5: Composition of matter

anything that occupies space and has mass

what is matter

• defined volume

• defined shape

• volume of solids is virtually independent of pressure and temperature

what are the key properties of solids

• fixed volume

• shape depends on the container

• volume of liquid is virtually independent of pressure and temperature

what are the key properties of liquids

• no fixed volume

• no fixed shape

• expands to completely fill container

• volume of gas is dependent on pressure and temperature

what are the key properties of gases

matter that has a constant composition - all samples of a pure substance have exactly the same makeup and properties

what is a pure substance

composed of two or more types of matter that can be present in varying amounts and be separated by physical changes

what is a mixture

a mixture with uniform composition and properties and appears the same visually throughout

what is a homogenous mixture (solution)

mixture that varies in composition or properties from point to point

what is a heterogenous mixture

• liquid-vapour curve

  • separates the liquid and gaseous regions of the phase diagram and provides the boiling point at any pressure

• solid-vapour curve

  • indicates the temperatures and pressures at which ice and water vapour are in equilibrium (as shown in fig 5.7)

  • corresponds to the sublimation/deposition points for water

• solid-liquid curve

  • shows the temperatures and pressures at which ice and liquid water are at equilibrium

  • represents the melting/freezing point of water

• critical point

  • this is the point of intersection of all three curves

  • at this point all three phases coexist in equilibrium

  • at pressures lower than the triple point, water cannot exist as a liquid, regardless of the temperature

describe the different points on a phase diagram

• matter is made of elements

• elements consist of only one type of tiny particles (atoms) with a characteristic mass

• a compound is a mixture of different elements bonded together in a specific mass ratio

what are the observations of Dalton’s atomic theory

• the characteristics of an element depend on its type of the smallest unit (atoms)

• a compound has unique properties due to its type of atoms and their fixed ratio

• chemical changes rearrange atoms but neither create nor destroy them

what are Dalton’s postulates on the atomic theory

All samples of a pure compound contain the same elements in the same proportion by mass

what is the law of fixed proportions

• protons (p+)

• neutrons (n)

  • protons and neutrons make up the nucleus

• electrons (e-)

what subatomic particles make up atoms

due to the mass of p+ and n in the nucleus

why do atoms have gravitational potential energy

due to the speed of the electrons that orbit the nucleus

why do atoms have kinetic energy

• innermost shell - up to 2e-

• outermost shell - up to 8e-

what are the occupancy limits of electron shells

all atoms are energetically most stable when they have 8 valence electrons as 4 pairs

what is the octet rule

• shiny

• conduct heat and electricity

• exist in different oxidations states

what are some properties of metals

alkali metals

what type of elements exist in group 1

alkaline earth metals

what type of elements exist in group 2

pnictogens

what type of elements exist in group 15

chalcogens

what type of elements exist in group 16

halogens

what type of elements exist in group 17

noble gases

what type of elements exist in group 18

highest energy level shell containing electrons

what is a valence shell/band

unoccupied energy levels

what is a conduction shell/band

the energy level of the valence shell and the number of valence electrons

what determines the characteristics of a material

1. N2 gas from the atmosphere is ‘fixed’ either by industrial processes to ammonia (NH3) directly or nitrogen fixing bacteria for uptake by plants or microbes or through lightning to nitrates

   • plants source nitrogen as either nitrate ions, ammonium ions, or urea, then animals source their nitrogen from plants or other animals

2. proteins made by animals or plants are either metabolised or excreted and ultimately experience decay which then leads them to be further metabolised into ammonia, NH3

3. under atmospheric conditions, ammonia is converted into nitrates, NO3-, they are then available to the root systems of plants

describe the nitrogen cycle