Download Chemistry I Lecture Notes – Atomic Structure

Chemistry I Lecture Notes – Atomic Structure
Dalton’s Atomic Theory (1808)
 All matter is made up of atoms.
 Atoms are indivisible (cannot be broken down into smaller
pieces!)
 All atoms of a given element are exactly alike in size, mass and
shape.
 Atoms of different elements can combine in simple whole
number ratios to form compounds.
 Atoms are simply just rearranged in chemical reactions.
Law of Definite Proportions
 Atoms combine in simple whole number ratios to form
compounds.
Law of Multiple Proportions
 Atoms of the same two (or more) given elements can
combine in different simple whole number ratios to form
different compounds. In other words, two or more
compounds can be composed of exactly the same
elements but they have differing ratios of each element
making them up.
Some Important Concepts:
Atomic Number – the number of protons that are in a given atom.
Atoms of the same element always have the same atomic number.
Elements are arranged in the order of increasing atomic number
on the Periodic Table.
Mass Number -- the number of protons + the number of neutrons
in a given atom of an element.
Average Atomic Mass – the weighted average of all of the isotopes
of a given element. This is what is found on the Periodic Table.
Structural Components of An Atom:
Proton – Positively charged particle found in the nucleus of an
atom. It is 1800 times larger than an electron.
Neutron – Neutral particle (no charge) found in the nucleus of an
atom. It is also 1800 times larger than an electron.
Electron – Negatively charged particle found outside the nucleus
of an atom within specific regions of space. It is 1800 times
smaller than a proton (or neutron). In comparison, the mass of an
electron is negligible in comparison. So the entire mass of an atom
is based on the mass of neutrons and protons.
Special Note:
In relatively recent history other subatomic
particles have been discovered which includes quarks, muons,
taumesons and gluons. We will concentrate our study on the three
primary subatomic particles being protons, neutrons and
electrons.