Atoms, Elements and Compounds
- There are about 100 different types of atoms & therefore only about 100 elements
- Some substances are made up of one type of atom --> These are called substance elements
- Elements contain only one type of atom
- Compounds contain more than one
- An atom has a tiny nucleus surrounded by electrons.
Different Types of elements:
The Alkali Metals- Very reactive, not found naturally.
The Alkaline Earth Metals- Very reactive (Oxidation number of +2), not found free in nature.
The Transition Metals- Ductile and Maleable, conduct electricty and heat.
The Halogens- Compounds containing Halogens are 'salts'. All halogens have 7 electrons in their outer shell, (Oxidation number of -1) They exist at room temprature in all 3 states of matter.
- Solid- Iodine, Astatine
- Liquid- Bromine
- Gas- Fluorine, Chlorine
Atoms, Elements and Compounds (Continued)
The Noble Gases- 'Inert gases' (Oxidation number of 0) This prevents them from forming compounds easily. Full outter shell of electrons making them stable.
- The Nucleus contains protons and neutrons.
- Atoms are made of protons, neutrons and electrons.
- Protons and electrons have equal and opposite electric charges.
- Atomic number =Number of Protons (=Number of Electrons)
- Mass number = Number of Protons + Neutrons
- Atoms are arranged in the Periodic tbale in order of their atomic number
Neutron 0 (Have no electrical charge. They are neutral)
The Arrangement of Electrons in Atoms
- The electrons in an atom are arranged in energy levels or shells.
- Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic table
- The number of electrons in the outer most shell of an element's atom determines the way that element reacts.
Electron Shell Diagrams
- The first shell can only hold 2 electrons
- Each shell after that can hold up to 8 electronsper shell.
When a metal bonds with a non-metal, the metal atom gives one or more electron to the non-metal atom. Both atoms become charged particles called ions.
- Metal atoms form positively charged ions (+)
- Non-metal atoms form negatively charged ions (-)
Opposite charges attract each other. There are stron attractions between the possitive and negative ions in a compound of a metal and non-metal. These strong forces of attraction are the chemical bonds that form. They are called ionic bonds.
In compounds between metals and non-metals, the charges on the ions always cancel each other out. This means their compound has no overall charge. Eg- Lithium Fluoride = LiF
Forming Bonds (Continued)
Non-metals bond in a different way. The outtermose shells overlap and they share electrons. This is called a Covalent Bond.
- No ions are formed
- They form molecules- Eg- hydrogen sulfide H2S and Methane CH4
Chemical equations show the products and the reactants. We can represent this using a word equation:
- Hydrogen + Oxygen -> Water
^Reactants = ^Products
Symbol equations helps us see how much of each substance is reacting.
- CaCO3 -> CaO + CO2
This equation is balanced- there is the same number of each type of atom on both sides of the equation. This means that- The total mass of the products formed in a reaction is equal to the total mass of reactants.
Chemical Equations (Continued)
- Word equations are only useful if everyone who reads them speaks the same language.
- Word equations do not tell us how much of each substance is involved in the reaction.
- Word equations can get very complicated when lots of chemicals are involved