ATOMS

An atom is the basic unit of life.

Atoms are extremely small

An atom is the smallest unit of matter An atom is the smallest unit of matter. Two or more atoms can bond together to form a molecule.

Atomic structure neutrons protons electrons

Neutron the neutron is in the nucleus or center of the atom

Proton the proton is also located in the center or nucleus of an atom

Electron the electrons orbit or circle outside the nucleus of an atom many billion times a second

NUCLEUS NEUTRON ELECTRON PROTON

Electrical Attraction between the POSITIVE nucleus and the NEGATIVE electrons keeps the electrons in orbit around the nucleus.

Electrons can orbit the nucleus in several different paths, or shells.

Each electron path can only hold a certain number of electrons.

Atoms can have as many as SEVEN shells

The different paths of electrons are labeled with letters.

The path nearest the nucleus is the K shell.

After the K shell, the others shells, in order, are called M, N, O, P, etc.

The path closest to the nucleus can hold only 2 electrons.

The second path holds 8, the third 18, and the remaining paths can each hold 32.

USUALLY shells will fill completely before starting a new shell.

The atom is more stable if each path is completely filled before a new path is started.

Protons and neutrons both have approximately the same atomic weight

Electrons have a much smaller atomic weight, and it would take over 1,800 electrons to equal the weight of one neutron or proton.

electrical charge of atom parts protons positive (+) neutrons neutral (none) electrons negative (-)

Bohr model Bohr was the first scientist to make a model with the neutron and proton in the center of the atom in the nucleus and the electrons circling outside the nucleus in orbits, called paths.

Atoms join together to form substances.

Some substances contain two or more different types of atoms, such as water.

Water is made of both oxygen and hydrogen atoms.

Other substances are made of only one type of atom that can not be broken into different types of atoms either chemically or physically.

These substances are called elements These substances are called elements. They are the simplest form of matter.

There are currently over 100 elements that have been identified.

90 of these elements occur naturally and 25 have been manufactured in labs by scientists.

The Periodic Table is a way scientists organized the elements.

They are grouped according to the number of protons in the elements’ nucleus.

Other information about the elements is also listed on the Periodic Table.

Periodic Table Information atomic number symbol element name mass number

The atomic number indicates how many protons are in an element.

The symbol is a short way of referring to the element.

For instance, instead of having to write nitrogen, a scientist would simply put N.

An element’s symbol is usually based on the Latin word for the element.

The symbol for iron, for example, is Fe because the Latin word for iron is ferrum.

Atomic number 79 Au Symbol Name Gold 197 Mass number

An element’s name can be different in different languages, but the element’s symbol always stays the same.

The mass number listed on the table is a total of the number of protons and neutrons an atom has.

With the help of the Periodic Table, scientists can tell at a glance the number of electrons, protons, and neutrons an element has.

The number of protons and electrons in an atom are the same.

The number of neutrons = the mass number - atomic number.

Take zinc, the atomic number ( # of protons) is 30 Take zinc, the atomic number ( # of protons) is 30. The Mass number (# of neutrons and protons) is 65. Therefore, there are 65-30 or 35 neutrons.

Chlorine (Cl) mass number = 35 atomic number = 17 # of neutrons= 18

Gold mass number=197 atomic number=79 # of neutrons= 118