E2 – E35

 An atom is the smallest unit of a pure substance that still has the properties of that substance.

 Nucleus – the center of an atom, it has a positive electric charge. Every nucleus has at least one proton.  Proton – a subatomic particle that has a positive electric charge.  Neutron – a subatomic particle that has no electric charge. (neutral)  Electron – a subatomic particle with a negative electric charge.

 The nucleus is a very dense region of an atom, made of protons and neutrons, at the center of an atom. The electrons circle the nucleus.

 The atomic number of an atom is determined by the number of protons in the nucleus.  Oxygen #8Hydrogen #1

 An element is a pure substance that’s made up of only one kind of atom. It cannot be broken down into other substances by ordinary laboratory methods.

 Metal – an element that conducts heat and electricity well. 75% of elements are metals. Metals are shiny.  Nonmetals – do not conduct electricity, and they are not shiny or malleable.  Malleable means that metal can be bent and rolled into sheets.

 Elements are arranged by their atomic number (protons in the nucleus).  Each square is an element.  The square contains the atomic number, chemical symbol, name, and atomic mass.  Elements are solids, liquids, and gases.  Families are in columns and have similar characteristics.

 Atoms often bond together and form larger units.  Molecules are units formed from two or more atoms.  Oxygen = two bonded oxygen atoms  Carbon Dioxide= one atom of carbon and two atoms of oxygen  The electrons circling the nucleus join together to form the bond.

 Solid- a definite shape and volume, molecules are held tightly in place.  Liquid – definite volume, but no definite shape, molecules are far apart  Gas – no definite shape or volume, molecules move around freely  Adding or taking away heat creates the changes of state.

 Plasma is a gas with ‘free’ electrons.  The core of a fire and the stars in the sky are both examples of plasma.

 Atoms become elements.  Elements become molecules.  Molecules become Compounds.

 A compound is a substance formed from the atoms of two or more elements.  Water - H 2 O  Table Salt – NaCl  Rust – Fe 2 O 3  Sugar – C 12 H 22 O 11

 An acid is a compound that reacts easily with other substances, and turns litmus paper red. They are very corrosive and can destroy body tissue.  A base is a compound that also reacts easily with other substances, but turns litmus paper blue. They are slippery and have a bitter taste.  Litmus paper is a small strip of paper inserted into a substance to test it’s acidity.

 The strength of an acid or base is measured on the pH scale.  pH 7 is neutral  pH 0-7 are acids  pH 7-14 are bases

 John Dalton – In the early 1800’s he determined that everything is made of atoms.  J.J. Thomson – there a negative electrons scattered in a positive sphere  Ernest Rutherford – an atom is mostly empty space with a tiny nucleus.  Niels Bohr – electrons move in ‘energy orbits’ around the nucleus

 Atomic Number = Number of Protons  Atomic Number = Number of Electrons  Number of Neutrons = Rounded Atomic Mass – Atomic Number  You must be able to look up the atomic mass, then round it!