Atomic Structure

• Atom: the smallest particle of matter, made up of electrons orbiting a nucleus of protons and neutrons.
• Element: a pure substance made up of one type of atom 118 elements.
• Elements are grouped by their properties in the periodic table.
• Atomic number: the number of protons in an atom.
• Period: a row in the periodic table.
• Group: a column in the periodic table.
• Mass number = number of protons + number of neutrons.
• All atoms are composed of: protons (+), neutrons (0) and electrons (-) (charge).
• The outermost shell of an atom is known as its valence shell.
• The electrons in the valence are involved in the formation of compounds.
• Valency refers to the number of electrons an atom will lose or gain to obtain a full outer shell.
• Ions are atoms that have gained or lost electrons.
• Positive ions have lost electrons (more protons than electrons) -cations.
• Negative ions have gained electrons (more electrons than protons) - anions.
• Elements are arranged into 18 groups, the vertical columns based on their physical and chemical properties.
• Groups indicate the number of valence (outermost) shell electrons.
• Group 1 - Alkali metals                             Group 17 - Halogens
• Group 2 - Alkaline earth metals              Group 18 - Noble gases
• Middle of table is transition metals
• Reactivity: How easily an element can obtain a full shell (to form a compound).
• Metals: are good conductors of heat and electricity, are shiny, malleable and ductile,  react with oxygen, water and acids (to certain degrees).
• Non-metals: can react with metals or themselves (halogens), are not reactive (noble gases), do not conduct electricity or heat, are dull and brittle
• Metalloids: have properties of both non-metals and metals.
• John Dalton proposed the atomic theory in 1808 which stated that all matter is made of tiny particles called atoms.
• John Newlands was the first person to arrange the 60 known elements in order of increasing mass in 1864.
• In 1869, Dmitri Mendeleev arranged the known elements in order of mass number, putting the known 'families' into vertical columns.
• Matter is anything that occupies space and has mass. In other words, matter is anything that has volume and mass.
• An element is a substance that cannot be made into anything simpler by means of a chemical reaction
• A compound is a substance that can be made into something smaller by means of a chemical reaction. Compounds contain more than one element. Compounds do not have the same properties as the elements they contain. Compounds are formed by chemical reactions, and (b) they have different properties from the elements they contain
• The existence of these particles is supported by some observations. Some examples are: (a) When a drop of ink falls into a glass of water, the colour of the ink spreads throughout the water. This shows that ink is made up of particles in motion
• A water molecule (H2O) consists of one oxygen and two hydrogen atoms, and a carbon dioxide molecule (CO2) consists of one carbon and two oxygen atoms.
• A molecule may also consist of dissimilar atoms of two or more elements.
• The particles in compounds may be molecules or ions.
• Molecules are made up of two or more atoms held together by chemical bonds.
• Quinine, a drug used to treat malaria patients, has the formula C20H24N2O2.
• Molecules are particles that are not charged.
• A molecule may consists of atoms of the same element, for example, oxygen molecules (O2), nitrogen molecules (N2), hydrogen molecules (H2) and sulphur molecules (S8 ).
• The atomic model is the ‘currently accepted’ model of the atom.
• Ancient Greeks (Democritus) proposed that all matter is made from invisible particles.
• Dalton's atomic model describes atoms as solid spheres that could come in different types, making different elements.