ATOMS

WHAT IS AN ATOM???• LET’S FIND OUT…• http://

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• 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, it 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)

• 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 proton’s are there? 8 How many electrons are there? 8

• The atomic mass atomic number is the sum of protons and number of neutrons.

• #p + #n = mass #• #n = mass # - atomic #

Because atoms are sooo small, we are unable to see them. Therefore, scientists make and use models to represent them. There are 2 models for atoms: 1. Bohr Model: Claimed that electrons moving

around the nucleus only travel in orbits like planets thus it was called a planetary model.

2. Electron Cloud Model: This is the current model we use today and 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.)

ATOMS COMBINE• Most matter is in the form of compounds or

mixtures of compounds. For example: Salt, water carbon dioxide (exhaled)

• Compounds have properties unlike those of their elements. For example: Salt (NaCl)- Sodium/Na is a shiny, soft, gray, explosive metal with water and 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 and the ratios of the atoms to those elements. For example: NaCl (salt) means there is 1 atom of sodium to (Na) to 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 a compound. It means “written below”. For example: H20 (2 is the subscript) There are 2 atoms of Hydrogen and 1 atom of Oxygen. This makes up 1 molecule of water.

• 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

• 2. Covalent Bond: The sharing of electrons between elements. It is NOT made of charged particles. Ex: H2O = Covalent Bond