Ch. 3: Atoms 3.1 Foundations

History  Democritus named the most basic particle named the most basic particle atom- means “indivisible atom- means “indivisible  Aristotle didn’t believe in atoms didn’t believe in atoms thought matter was continuous thought matter was continuous

History  by 1700s, all chemists agreed: on the existence of atoms on the existence of atoms that atoms combined to make compounds that atoms combined to make compounds  Still did not agree on whether elements combined in the same ratio when making a compound

Law of Conservation of Mass  mass is neither created or destroyed during regular chemical or physical changes

Law of Definite Proportions  any amount of a compound contains the same element in the same proportions by mass No matter where the copper carbonate is used, it still has the same composition

Law of Multiple Proportions  applies when 2 or more elements combine to make more than one type of compound  the mass ratios of the second element simplify to small whole numbers

Law of Multiple Proportions

Dalton’s Atomic Theory 1. All mass is made of atoms 2. Atoms of same element have the same size, mass, and properties 3. Atoms can’t be subdivided, created or destroyed 4. Atoms of different element combine in whole number ratios to make compounds 5. In chemical reactions, atoms are combined, separated, and rearranged.

Modern Atomic Theory  Some parts of Dalton’s theory were wrong: atoms are divisible into smaller particles (subatomic particles) atoms are divisible into smaller particles (subatomic particles) atoms of the same element can have different masses (isotopes) atoms of the same element can have different masses (isotopes)  Most important parts of atomic theory: all matter is made of atoms all matter is made of atoms atoms of different elements have different properties atoms of different elements have different properties

Ch. 3: Atoms 3.2 Structure of Atom

Structure of Atom  Nucleus: contains protons and neutrons contains protons and neutrons takes up very little space takes up very little space  Electron Cloud: contains electrons contains electrons takes up most of space takes up most of space

Subatomic Particles  includes all particles inside atom proton proton electron electron neutron neutron  charge on protons and electrons are equal but opposite  to make an atom neutral, need equal numbers of protons and electrons

Subatomic Particles  number of protons identifies the atom as a certain element  protons and neutrons are about same size  electrons are much smaller  nuclear force- when particles in the nucleus get very close, they have a strong attraction proton + proton proton + proton proton + neutron proton + neutron neutron + neutron neutron + neutron

Atomic Radius  size of atom  measured from center of nucleus to outside of electron cloud  expressed in picometers (10 12 pm = 1 m)  usually pm

Example  An atom has a radius of 140 pm. How large is that in meters?