ATOMS, ELEMNTS AND COMPOUNDS Atomic Structure and the Periodic Table PARTICLE RELATIVE CHARGE MASS (ATOMIC MASS) Proton +1 1 Neutron 0 1 Electron -1 1 1836 • Proton/Atomic number: o Number of protons in an atom (or number of electrons in atom) • Nucleon/Mass number: o Number of protons + Number of neutrons of an atom • In the periodic table, o The proton number increases by 1 when you go to the right o When you go one element down, you increase proton number by 8 in the first 3 periods (transition elements not included) • Isotopes: o Atoms of the same element with different number of neutrons o Ex: Carbon 12 and Carbon 14 o There are two types in isotopes: ▪ Non-radioactive isotopes ▪ Radioactive isotopes – unstable atoms that break down giving out radiations o Medical use: ▪ Cancer treatment (radiotherapy) – the rays will kill the cancer cells using Cobalt-60 o Industrial use: ▪ To check for leaks – radioisotopes (tracers) added to oil/gas. At leaks, radiation is detected using a Geiger counter. • Electrons are arranged in electron shells/energy levels. • Atoms want to have full outer shells (full set of valency electrons), this is why they react. • Noble gases have full outer shells, so they don’t need to react. • Electron shell structure: 2,8,8,18. • More reactive elements have a greater desire to have a full outer shell, so also form more stable compounds. Bonding: The Structure of Matter • Element: o A substance that cannot be split into anything simpler, in a chemical reaction. Each element has a unique proton/atomic number. • Mixture: o Two or more elements mixed but physically and not chemically. • Compound: o A substance in which two or more elements are chemically combined. METALS NON-METALS Strong Brittle Good conductors of electricity and heat Poor conductors of electricity and heat (except graphite) High melting and boiling points Lower melting and boiling points than metals High density Low density Forms basic oxides Forms acidic oxides Forms cations in reactions Forms anions in reactions Malleable and ductile Non-malleable and non-ductile Sonorous Non-sonorous Some are magnetic Magnetic if they have an electric charge • Alloy: o Mixture of two or more metals or mixture of one or more metal with a nonmetal, to improve its properties. o Ex: ▪ Brass – Copper (Cu) and Zinc (Zn) ▪ Steel – Iron (Fe) with non-metallic Carbon (C) ▪ Red gold – Gold (Au) and Copper (Cu) ▪ White gold – Gold (Au) and Silver (Ag) Ions and Ionic Bonds • • • • Chemical bond is formed by transfer of electrons from one atom to another. Metals lose electrons to form cations and non-metals gain electrons to form anions. Positive cations and negative anions attract to each other. Strong electrostatic force of attraction between positive cations and negative anions is called ionic bonding. PROPERTIES REASON Forms a giant lattice Cations and anions attract High melting and boiling points Strong bons between ions Do not conduct electricity when solid Ions aren’t mobile/cannot move Conduct electricity when molten/aqueous Ions are mobile/can move Usually soluble in water Not required Molecules and Covalent Bonds • When atoms share electrons to obtain a noble gas electron structure, covalent bonding arises. • Covalent bonding takes place between non-metals only. SINGLE BOND DOUBLE BOND TRIPLE BOND H)H O=O N≡N 2 electrons shared (1 from each atom) 4 electrons shared (2 from each atom) 6 electrons shared (3 from each atom) PROPERTIES REASON Low melting and boiling points Weak intermolecular forces of attraction between molecules Usually liquid, gas or a solid with a low melting point Weak intermolecular forces of attraction between molecules Don’t conduct electricity No mobile ions/electrons Usually insoluble in water Not required Example: Macromolecules DIAMOND GRAPHITE • Four bonds • High melting point • Does not conduct electricity but it conducts heat • Used for cutting as it is known as the strongest known substance • Three bonds • Made of flat sheets • Held together by weak forces so it is soft and is used as a lubricant • Conduct electricity as it has one free electron SILICON DIOXIDE • Makes up sand • Each Si (Silicon) is bonded to 4 oxygen atoms, and each oxygen is bonded to 2 silicon atoms • So, it has a high melting point and is hard like diamond • Melting point is high as the structure is made up of strong covalent bonds. • It does not conduct electricity as it doesn’t have mobile ions/electrons. (except for graphite) • It is hard as it exists in tetrahedral structure, but graphite is soft. Metallic Bonding • Delocalized electrons (free electrons/ sea of mobile electrons) can carry charge. Hence metals are conductors of electricity and heat. • The strong electrostatic forces of attraction between the positive metal cations and the delocalized electrons are called as metallic bonds. • The layers are held together by the delocalized electrons. When force is applied, these electrons act like glue holding the structure in shape. Hence metals are malleable and ductile. • Positive ions held together by electrons – acts like glue.
