Atoms

Review: Matter is anything that takes up space (has volume) and has weight (has mass).

What is most matter made of? Most matter is made up of molecules. What are molecules made of? Molecules are made of ATOMS.

So what’s an atom?? An atom is the smallest unit that all matter is made up of. Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.

A closer look at an atom An atom has three parts: Protons = positive charge (+) Neutrons = neutral (no) charge (+/-) Electrons = negative charge (-) The protons & neutrons are found in the center of the atom, a place called the nucleus. The electrons orbit the nucleus

Atomic Fact # 1: No matter is made up of protons alone. No matter is made up of neutrons alone. No matter is made up of electrons alone. In other words…..no matter is made unless these parts are joined together to make up an atom. It’s the atoms that build matter, not the atom’s parts alone.

Atomic Fact # 2: The number of protons ALWAYS equals the number of electrons.. The number of positive charges ALWAYS equals the number of negative charges in an atom. So what does that mean about the charges? So then what kind of charge do atoms have? Atoms have a neutral charge (no charge) since they have equal amounts of positive and negative charges.

Atom Models There are two models of the atoms: Bohr Model Electron Cloud Model Although the Electron Cloud Model is the most recent model, in class we will be using the Bohr model since it shows important information about the electrons.

Bohr Model The Bohr Model shows all of the particles in the atom. In the center are circles. Each circle represents a single neutron or proton. Protons should have a plus written on them. Neutrons should be blank. In a circle around the nucleus are the electrons. Electrons should have a minus sign

Electrons have special rules…. You can’t just shove all of the electrons into the first orbit of an electron. Electrons live in something called shells or energy levels. Only so many electrons can be in any certain shell. The outer most shell is called the valance shell. The electrons in the outer most shell of any element are called valance electrons.

Nucleus 1 st shell 2 nd shell 3 rd shell

So let’s draw this in our notebooks….

Since atoms are so small, is it easy to break them apart? No. The forces holding atoms together are extremely strong (which is good because if they were weak then everything we know that’s matter could fall apart easily). Breaking open an atom’s nucleus releases energy from that nucleus called nuclear energy. Nuclear energy is extremely powerful and is used in making nuclear weapons.