Atoms
The smallest particles of matter
Different types of atoms exist for every type of matter
From Greek for invisible
Democritus- world made of empty space and tiny particles -wrote our
current definition of atoms over 1500 years ago.
The idea that matter is made of fundamental particles called atoms is
known as the atomic theory of matter.
1782-Lavoisier did experiments that resulted in the law of
conservation of matter/mass.
1799-Proust did more experiments and found that the elements that
composed the compounds were always in a certain proportion by
mass. This is the Law of Definite proportions.
1803-Dalton
Atomic Theory of Matter
1. All matter is made of atoms
2. Atoms are indestructible and cannot be divided into smaller pieces
(atoms are invisible)
3. All atoms of one element are exactly alike, but they are different
from atoms of other elements
This gave chemists a model of the particle nature of matter
In the late 19th century experiments began to suggest that atoms are
made of even smaller particles.
Atomic Structure
Electrons- Invisible, Negatively charged particles (smallest pieces of
atoms)
Protons- positively charged particles
Neutrons- neutral particle
Nucleus- dense, positively charged central core
-protons and neutrons
Atomic Number
The number of protons in the nucleus of that element.
Knowing this, how many protons are in the nucleus of Carbon?
Potassium?
Lithium?
Mercury?
Iodine?
The number of protons determines the identity of that element, as well
as many of it's chemical and physical properties.
Because atoms have no overall electric charge, an atom must have as
many electrons as it has protons in it's nucleus.
So the atomic number of a NEUTRAL atom also tells the number of
electrons in an atom of that element.
How many electrons are there in an atom of Xenon?
Sulfur?
Copper?
Iron?
Sodium?
Neutrons are also found in the nucleus of atoms.
Protons and Neutrons weigh about the same amount, 1 atomic mass
unit (amu), while electrons weigh much less, 0.00055 amu.
The sum of the protons and neutrons in the nucleus is the mass
number.
(electron weight is negligible)
So the mass number = protons + Neutrons
For Oxygen:
15.99 = 8 + N
7.99 = N
We cannot have a part of a neutron, so we round to 8.
There are 8 protons and 8 neutrons in an atom of Oxygen.
Because this atom is neutral we know that there must also be 8
electrons.
How many Protons, Neutrons, and Electrons in Nitrogen?
Neon?
Calcium?
Cesium?
Gold?
Nickle?