Atomic Structure

Atom Atoms are made of: Nucleus Electron shells Makes up 99.99% of the atoms mass, but only 0.01% of the atoms volume. Protons Positively charged particles (p+) Neutrons Neutrally charged particles (n0) Electron shells Electrons Negatively charged particles (e-) Smallest particle in the atom.

Atomic mass Mass in AMU (atomic mass units) Mass in grams Electrons = 0 amu (actually 1/1840) Neutrons = 1 amu Protons = 1 amu Mass in grams Electron = 9.11 x 10-28 grams Neutron = 1.67 x 10-24 grams Proton = 1.67 x 10-24 grams

N Atomic Number 7 Main number on each element on the periodic table. Equals the number of protons in an atom. Nitrogen has an atomic number of 7. It has 7 protons. N 7 14.0067

Mass Number The mass number is equal to the number of protons plus the number of neutrons. Mass number = protons + neutrons Mass number on the periodic table is the average atomic mass. Atoms may contain more or less neutrons. These are called isotopes. The average atomic mass is an average of all the isotopes and how common they are. N 7 14.0067 The average atomic mass of nitrogen is 14.0067. Its most common isotope has a mass of 14. 7 protons + 7 neutrons = 14

Isotopes Atoms of the same element can have different numbers of neutrons. different mass numbers. called isotopes.

X Symbols Mass number Atomic number Contain the symbol of the element, the mass number and the atomic number. Mass number X Atomic number

Naming Isotopes Put the mass number after the name of the element. carbon- 12 carbon -14 uranium-235

Na Symbols 24 11 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 24 Na 11

Br Symbols 80 35 Find the number of protons number of neutrons number of electrons Atomic number Mass Number Name 80 Br 35

Practice: Fe 30 5 11 20 21 Cu 29 65 Element name Symbol Atomic # # of Protons # of Electrons # of Neutrons Mass number Fe 30 5 11 20 21 Cu 29 65

Electrons = protons - charge The number of electrons in a neutral atom is equal to the number of protons. In an ion, the number of electrons is equal to the protons minus the charge. Electrons = protons - charge

Valence Electrons Electrons in the outer most shell. All atoms want 8 valence electrons. They can either lose the electrons they have, or gain extra electrons. They do this by bonding with other atoms. The number of valence electrons are determined by the column on the periodic table.

Valence Electrons 1 Valence electron 8 Valence electrons Valence electrons of the Transition metals vary

Dot Notation Dot notation shows the valence electrons placed around the symbol of the element. The electrons are placed in the following order. 3 6 X 4 1 7 2 5 8

. : : S . For Example Sulfur: Try the following: Aluminum Chlorine Arsenic

Electron Configuration Electron configuration shows the energy level and orbital of every electron in an atom. The energy levels are known by the rows on the periodic table.

Energy Levels 1st energy level 2nd energy level 3rd energy level 4th energy level 4th energy level 5th energy level 6th energy level 7th energy level 4th energy level 5th energy level

Orbitals Orbitals are the shaped areas where the electrons are found.

S P D F Orbitals S orbital can hold 2 electrons P orbital can hold 6 electrons D orbital can hold 10 electrons F orbital can hold 14 electrons S P D F

Example The electron configuration for Bromine: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 Use the periodic table to write the electron configuration. Try the following: Nitrogen Calcium Cesium

Bohr Models The Bohr model is a visual representation of the atom. The protons and neutrons are written as the nucleus of the atom. The electrons are placed around the nucleus using the electron configuration. Let me show you.

Maximum electrons The first energy level can hold 2 electrons The second holds 8 The 3rd holds 18 The fourth holds 32 The 5th holds 32

Molar Mass First look at the formula for the compound. Multiply the number of each atom by the mass of each atom. The sum of the masses will be the mass of the compound (molar mass) Example: CaF2 1 Ca @ 40.1 = 40.1 2 F @ 19.0 = 38.0 Molar mass = 78.1

Practice What is the molar mass of the following compounds? Sodium chloride 58.5 Magnesium Bromide 184.1 Carbon dioxide 44.0 Aluminum sulfate 342.3 Al2(SO4)3 2 Al @ 27.0 = 54.0 3 S @ 32.1 = 96.3 12 O @ 16.0 = 192.0 Molar mass = 342.3