MIXTURES

Atoms

•Atoms are the smallest pieces of matter (stuff) that can exist by themselves. They have three main parts:

–Neutrons (neutral, no charge) – in the nucleus.

–Protons (positive) – in the nucleus

–Electrons (negative) surround the nucleus in groups called shells

The number of protons (+) and electrons (-) in an atom is always the same 

Element

•An element is something made of one type of atom.

–It has a specific number of protons (same as the atomic number).

–The Atomic Mass tells you the average number of protons and neutrons in the atom

•Elements and their symbols are found on the Periodic Table.

–Some elements exist on their own as single atoms (eg Helium), others exist as pairs of atoms (eg oxygen molecule).

Compounds

•Compounds are made of >1 type of atom, in specific ratios, which are chemically bonded together.

–Eg Every water molecule contains 2 hydrogens and 1 oxygen. If it has more or less, then it is NOT water.

•Ionic compounds: Typically a metal and non-metal(s).

–The metal loses an electron, becomes +ve ion (cation)

–The non-metal gains an electron, becomes –ve ion (anion)

–Compound held together by attaction of opposite charges

•Covalent compounds: Typically only non-metals.

–Electrons are (usually) evenly shared

Elements and Compounds

•Elements and compounds are both pure substances.

•This means they have fixed (consistent) physical and chemical properties.

–Eg Water (H2O) always boils at 100oC, 1cm3 of water always weighs 1g

–Eg Sugar (C6H12O6) always melts at 146oC, 1cm3 of glucose always weighs 1.5g

•Compounds usually have very different properties to the elements that make them up.

–Eg Hydrogen and oxygen are flammable gases but water is a non-flammable liquid

Mixtures

•A mixture is made of 2 or more substances which are not chemically bonded together.

•Mixtures are impure substances, meaning they do not have fixed (consistent) properties

–Eg All cups of tea taste differently because they have different amounts of tea, sugar and milk.

•The components can be separated based on their individual physical properties (boiling point, density, particle size, magnetism).

Homogenous Mixtures

•Homo = same throughout

•Solutions = contain a solute (material which is dissolved) and solvent (material which dissolves something else).

–Solute particles are <1nm

–Solute passes through filter paper

–Solute doesn’t separate on standing.

–Transparent: they do NOT scatter light, even if coloured. 

–Note: If the solvent is water, we have an AQUEOUS solution.

•Colloids = microscopic particles evenly dispersed in another material.

•Includes gels, sols and emulsions

–Particles are 1 – 100nm

–Particles passes through filter paper

–Particles don’t separate on standing.

–They DO scatter light (Tyndall effect).

Note: Some references state colloids are heterogeneous

Heterogeneous Mixtures

•Hetero = different / uneven throughout

•Suspensions = larger particles (>100nm) dispersed unevenly throughout a liquid.

–The particles will settle on standing.

–Filtration may remove some of the particles