Elements, Mixtures & Compounds Syllabus objectives: Describe the differences between elements, compounds and mixtures State the symbols of the elements and formulae of the compounds mentioned in the syllabus. Deduce the formulae of simple compounds from the relative numbers of atoms present and vice versa.

Types of particles Particles Ions Atoms Molecules

Atoms and Molecules Matter is made up of tiny particles. These particles are called atoms. Atoms are the smallest particle of an element that can still have the chemical properties of that element. A molecule is made up of two or more atoms chemically joined together by covalent bond. (Can a molecule be joined together by ionic bonds?) Some substances exist as atoms while others exist as molecules.

Atoms and Molecules Examples of substances that exist as atoms All metals e.g. Gold (Au), Copper (Cu) Noble gases e.g. helium (He), neon (Ne) E.g. helium

Atoms and Molecules Examples of substances that exist as molecules Diatomic molecules eg. oxygen (O2) hydrogen(H2) hydrogen chloride (HCl) Tri-atomic molecules eg. water (H2O), Carbon dioxide (CO2)

Atoms and Molecules Atoms of the same element that are chemically joined together form molecules of elements. Atoms of different elements that are chemically joined together form molecules of compounds. element compound compound element

Examples of substances that exist as molecules :- Nitrogen gas (N2) Bromine liquid (Br2) These are ELEMENTS ! Hydrogen gas (H2) Oxygen gas (O2) Chlorine gas (Cl2)

Examples of substances that exist as molecules :- Carbon dioxide gas(CO2) Water(H2O) Ammonia gas (NH3) Methane gas(CH4) These are COMPOUNDS !

Elements An element is a substance which which cannot be broken down into simpler substances by chemical means. Elements contain only one type of atom. Egs. Aluminium, carbon, sulfur

Al C Cu Hg S Elements Elements are represented by symbols Examples.. Aluminium Carbon Copper Mercury Sulfur

Metals & Non-metals Elements can be classified as metals or non-metals Shiny Solids at r.t.p. (except Hg) Malleable and ductile High melting pt. & boiling pt. Good conductors of heat Good conductors of electricity dull Either gases, liquids or solids at r.t.p. brittle low melting pt. & boiling pt. (except C) Poor conductors of heat Poor conductors of electricity (except graphite)

Compounds A compound is a substance which is made up of 2 or more elements chemically combined together. Compounds contain only one type of molecule E.g.s. Water (H2O), common salt (NaCl), carbon dioxide (CO2)

Compounds A chemical reaction takes place when a compound is formed.

Compounds A chemical reaction takes place when a compound is formed. oxygen ( (silvery solid) a bright white light; ELEMENTS COMPOUND magnesium oxide colourless gas) magnesium magnesium burns with

Compounds A chemical reaction takes place when a compound is formed. ELEMENTS COMPOUND lighted splint hydrogen oxygen (colourless gas) colourless gas) heat, light water

Mixtures A mixture contains 2 or more substances which can be easily separated by physical means. Mixtures contain two or more types of atoms or molecules (physical means include : filtration, evaporation, distillation, chromatography etc.)

Representing atoms, molecules, elements, mixtures and compounds:

Representing atoms, molecules, elements, mixtures and compounds:

Representing atoms, molecules, elements, mixtures and compounds:

How do we deduce the formulae? Molecular Formulae How do we deduce the formulae? With the presence of both metallic and non-metallic elements, write the metallic element first. E.g. CaO, NaCl, FeS. Number of atoms is written as a subscript except for “1”. E.g. FeCl2 (not Fe1Cl2); K2Cr2O7 (not K2Cr2O7) Write oxygen atom at the end of the formula. E.g. H2O, CuO, MgCO3

Naming of compounds -ide: The compound has only 2 elements. Sodium chloride (NaCl) Iron (II) Sulfide (FeS) -Hydroxide: The compound has OH- ion. Sodium hydroxide (NaOH) Ammonium hydroxide (NH4OH) -ate or -ite: The compound has element oxygen. The former one has more oxygen atoms than the latter one. Sodium nitrate (NaNO3) & sodium nitrite (NaNO2)

Chemical Formula provides information about the type of element present in the compound the relative number of atoms (ratio) present Eg. (NH4)2SO4 contains.. CuSO4.5H2O contains…