Download Neutron - Piscataway High School

.CH #4 study guide
Atom: the smallest particle of an element that retains the properties of that element
Atomic mass: the weighted average of the masses of the isotopes of an element
Atomic mass unit: one-twelfth the mass of a carbon atom having 6 protons and 6 neutrons
Atomic number: the number of protons in the nucleus of an atom
Electron: a negatively charged subatomic particle
Isotope: atoms with the same number of protons, but different number of neutrons in the nucleus of an atom
Mass number: the total number of protons and neutrons in the nucleus of an atom
Neutron: a subatomic particle with no charge
Nucleus: the central part of an atom, containing protons and neutrons
Proton: a positively charged subatomic particle
Know Dalton’s atomic theory.
1. All elements are composed of tiny indivisible particles called atoms.
2. Atoms of the same element are identical
3. Atoms of different elements can physically mix or chemically combine in simple whole-number ratios.
4. Chemical reactions occur when atoms are separated, joined, or rearranged.
Know Democritus’ theory
Democritus believed that atoms were indivisible and indestructible
Know Rutherford’s experiment and conclusions
 Rutherford shot alpha particles at a sheet of gold foil
 Most particles went straight through, some particles were deflected, and others straight back.
 This proved that there was a small dense center called a nucleus that had a positive charge and that most of the
atoms was empty space.
Size of atomic nuclei
 5X10-11m to 2X10-10m
Know the size of the protons, neutrons, and electrons
 Proton: positive one charge; 1 atomic mass unit, +1
 Electron: negative one charge; 1/1840 amu or “0”, -1
 Neutron: Neutral charge; 1 atomic mass unit
Why are all atoms neutral?
 The number of electrons equals the number of protons
Explain the nucleus: make-up of particles as well as charge
 The nucleus contains protons and neutrons.
 The charge of the nucleus is positive
How do you find the number of protons? Electrons? And neutrons?
 Protons equals the atomic number
 Electrons equals the number of protons
 Neutrons equals the mass number –atomic number
How is atomic mass calculated?
 Atomic mass is calculated by taking the mass number of each isotope and multiplying it by the percent abundance
of each isotope as a decimal number. Then add all the isotopes together to get an atomic mass of that element
Find percent abundance
 Take the total number of particles of one isotope and divide it by the total number of particles of all the isotopes
Explain how one atoms of one element are different from another.
 Every element has an atomic number. Atoms of one element are different from one another by the different
number of protons and the atomic number.
How are 2 isotopes of the same element different from each other?
 Two isotopes are different from one another by:
o Number of neutrons
o Mass number
Why do isotopes have the same chemical behavior?
 Some isotopes have the same chemical behavior because they have the same atomic number, number of protons,
and number of electrons. The valence electrons give the element their chemical behavior.