Elements, Compounds, and Mixtures

Elements Made up of only one type of atom Can exist as a single atom or as a molecule Molecule: two or more atoms held together by a chemical bond Examples: He, O2, N2

Atoms Each element has a specific atom An atom has 3 main parts: Protons: positively charged part of an atom. Has a mass of 1 amu (atomic mass unit) Neutrons: part of an atom with no charge. Has a mass of 1 amu. Electrons: negatively charged part of an atom. Mass is too small to measure (~0 amu) Protons and neutrons are in the nucleus. Electrons rapidly orbit the nucleus in layers called energy levels

Compounds When atoms of different elements join together by chemical bonds Always exist as molecules (in same ratio) Properties are different from the component elements Examples: H2O, CO2, C6H12O6

Mixtures When more than one substance are mixed together. Can be made from elements &/or compounds The substances do not join chemically and keep their own properties Substances can be separated out of mixture. Ex: bag of skittles, air

Periodic Table A chart organizing information about all known elements Periods- the rows of the periodic table Corresponds to electron energy levels Groups- the columns of the periodic table Atoms in the same group have the same set up of their outer (valence) electrons Elements in the same group behave similarly

Atomic Arrangement- nucleus Protons and neutrons are located in the nucleus # protons = atomic number (defines the element) # neutrons = atomic mass – atomic number Round to the whole # for atomic mass. The number is a decimal because it’s an average. Isotope- atoms with the same number of protons, but different number of neutrons.

Atomic arrangement- energy levels Electrons are found orbiting the nucleus in a path called an orbital, in layers called energy levels. The number of electrons is equal to the number of protons. Elements in the first period of the PT have 1 layer of electrons. This layer can hold up to 2 electrons.

Energy levels continued Elements in the second period of the PT have 2 layers of electrons. This 2nd layer can hold up to 8 electrons.

Energy Levels continued Elements in the third period of the PT have 3 layers of electrons. This 3rd layer can hold up to 8 electrons.

Valence electrons Electrons in the outer layer or shell are called valence electrons. Atoms want to gain or lose electrons in order to have a full outer layer. When an atom gains or loses an electron, the charged atom is called an ion. Anion: An atom that has gained an electron and has a negative charge (-ide) Cation: An atom that has lost an electron and has a positive charge

Bonding Atoms form bonds to complete their outer layer of electrons and become neutral. Ionic bond: when oppositely charged ions attract forming an ionic compound Covalent bond: when atoms share one or more PAIRS of electrons (give one, get one). This happens when both atoms have almost full outer shells.