Download Study Guide - Chapter 11

Study Guide Chapter 11 – Introduction to Atoms
Section 1 – Development of the Atomic Theory
Democritus – if you cut something, you eventually end up with a particle that can’t be cut
A. Atom comes from the Greek word “Atomos”, meaning “not able to be divided”
Atom – the smallest particle into which an element can be divided and still be the same substance.
Dalton – developed an atomic theory
A. All substances are made of atoms
B. Atoms are small particles that cannot be created, divided or destroyed
C. Atoms of the same element are exactly alike
D. Atoms of different elements are different
E. Atoms join with other atoms to make new substances
Thomson – discovered there are small particles inside the atom called electrons
A. Plum pudding model – electrons mixed throughout the atom
Rutherford – discovered that atoms are mostly empty space with a dense, positive nucleus
Nucleus – an atom’s central region, which is made up of protons and neutrons
Bohr Model - electrons move around the nucleus in certain paths called energy levels
Electron cloud – a region around the nucleus of an atom where electrons are likely to be found (this is current theory)
Section 2 - The Atom
Nucleus
A. Protons – positively charged particles in the nucleus
1. Atomic mass unit – the SI unit of mass that describes the mass of an atom
A. Proton has a mass of 1 amu
B. Neutron has a mass of 1 amu
C. It takes more than 1800 electrons to equal the mass of 1 proton
B. Neutrons – particles of the nucleus that have no charge
Electrons – negatively charge particles found around the nucleus in electron clouds
Ion – if the charges are not equal between protons and electrons, you have a charge particle
Atomic number – the number of protons in the nucleus of an atom
A. The atomic number is the same for all atoms of an element
Isotope – atoms that have the same number of protons but have different number numbers of neutrons
A. They have the same atomic number but different atomic mass
Radioactive – an isotope that is an atom with a nucleus that will change over time
A. They spontaneously fall apart over time
B. They give off particles and energy
Mass number – the sum of the numbers of protons and neutrons in the nucleus of an atom
Atomic mass – the weighted average of the masses of natural isotopes of an element
Forces in the atom
A. Gravitational Force – pulls objects towards each other
B. Electromagnetic force – opposite charges attract and same charges repel
1. force that holds electrons around the nucleus
C. Strong Force – keeps a nucleus with 2 or more protons from flying apart
D. Weak Force – allows a neutron to change into a proton or electrons in certain unstable atoms