ATOMS

The smallest particle of an element that has properties of that element is called the ATOM. It is the BASIC BUILDING BLOCK OF ALL MATTER. An atom that has no charge; it’s neither positive or negative is called a NEUTRAL ATOM.

The atom is made up of 3 parts or subatomic particles. They are the PROTON, ELECTRON, and NEUTRON.

The PROTON has a positive charge (+), is found in the NUCLEUS, and has a mass of 1. The NEUTRON is neutral, is found in the NUCLEUS, and has a mass of 1. The ELECTRON has a negative charge (-), moves around the nucleus, and has a mass of 0.

The NUCLEUS is the positively charged center of an atom. Since atoms are neutral, the protons need to balance electrons. Therefore, the number of protons = the number of electrons (p’s = e’s) Atoms and Bonding Video (1:40)Atoms and Bonding Video

The Structure and Scale of Atoms Video (2:46)Video

The ATOMIC NUMBER is the number of protons in the nucleus of an atom. For example: Carbon’s atomic number is 6. So, there are 6 protons in the nucleus. Oxygen has an atomic number of 8. How many protons are there? 8 How many electrons are there? 8

The MASS NUMBER or ATOMIC MASS is the sum of the number of protons and number of neutrons. #p + #n = mass # #n = mass # - atomic #

Because atoms are soo small, we are unable to see them. Therefore, scientists make and use MODELS to represent them. There are 2 models for atoms.

BOHR MODEL Claimed that electrons moving around the nucleus only travel in orbits like planets thus it was called a PLANETARY MODEL Bohr’s model of the atom video (00:52)Bohr’s model of the atom video

ELECTRON CLOUD MODEL This is the current model we use today & is more accurate. It says that electrons are found in a “cloud” around the nucleus (kind of like the spray of water from a sprinkler, each drop represents where an electron might be). Electron Cloud Model Video (00:33)Electron Cloud Model Video

ATOMS COMBINE Most matter is in the form of COMPOUNDS or mixtures of compounds. For example: salt (NaCl), water (H 2 0), carbon dioxide (CO 2 ) Compounds have properties UNLIKE those of their elements. For example: Salt—Sodium (Na) is a shiny, soft, gray, explosive metal with water & Chlorine (Cl) is a yellowish-green gas that can kill but when they combine, it forms sodium chloride or table salt.

A CHEMICAL FORMULA tells what elements make up a compound & the ratios of the atoms to those elements. For example: NaCl (salt) means there is 1 atom of sodium (Na) to every 1 atom of chlorine (Cl).

A SUBSCRIPT is a number in a chemical formula written after a chemical symbol that tells how many atoms of an element there are in the compound. It means “written below”. For example: H 2 0 (2 is the subscript) There are 2 atoms of hydrogen (H) and 1 atom of oxygen (O). This makes up 1 molecule of water.

Video on Compounds Video on Compounds (3:59)

A CHEMICAL BOND is a force that holds atoms together in a compound. They use electrons to bond. There are 2 types of bonds.

1. IONIC BOND The transfer of electrons from one element to another. It is made of charged particles (+ and – atoms). Example: Na(+)Cl (-) = ionic bond/compound

Ionic Bonding video (2:18)

2. COVALENT BOND The sharing of electrons between elements. It is NOT made of charged particles. Example: H 2 O = covalent compound Covalent Bonds Video (1:23)Covalent Bonds Video

Covalent Bonds video (1:23)

PHYSICAL CHANGES ANY CHANGE IN MATTER THAT DOES NOT CHANGE THE IDENTITY OF THE MATTER EXAMPLES: CUTTING, GRINDING, CHANGING THE STATE (MELTING, FREEZING, ETC.)

CHEMICAL CHANGES CHANGE IN MATTER IN WHICH ONE SUBSTANCE IS CHANGED INTO ANOTHER SUBSTANCE. EXAMPLES: BURNING, RUSTING Chemical Changes vs. Physical Changes Video (1:52)Chemical Changes vs. Physical Changes Video (1:52)

Chemical Changes vs. Physical Changes video (1:52)

EVIDENCE OF A CHEMICAL CHANGE/REACTION: COLOR CHANGE PRECIPITATE FORMED HEAT PRODUCED OR REQUIRED GAS GIVEN OFF Evidence of Reactions Video (2:44)Evidence of Reactions Video

Evidence of Reactions video (2:44)