1. Protons & Valence Electrons 8.5B: Identify that protons determine an element’s identity, valence electrons determine its chemical properties, including reactivity

2. Protons Protons are positively-charged, subatomic particles found in the nucleus of an atom. They contribute to the mass of an atom. They ARE the IDENTITY of the atom. The number of protons does not change. The atomic number IS the number of protons An atom with 8 protons is ALWAYS Oxygen

3. Protons are the Identity of Atoms Each element has a unique number of protons in all of its atoms. The atomic number of an element is the number of protons in each of its atoms. To identify which element a model of an atom is depicting, count the number of protons in the nucleus and find the element on the periodic table with that number. Can you identify these atoms?

4. Valence Electrons Valence electrons are the electrons in the outermost energy level or orbital. They determine an atom’s reactivity. This Carbon atom has four valence electrons.

5. Reactivity Reactivity is the rate at which a chemical substance tends to undergo a chemical reaction (bond with other atoms) Lithium reacting with water

6. Valence Electrons In the Bohr Model of the atom, electrons fill different electron energy levels from the inside out. The first orbital can only hold two electrons. The second orbital can hold eight electrons, and the third can hold up to eighteen, but the outermost energy level can never have more that eight electrons. Only these outermost electrons, known as valence electrons, can interact with other atoms in chemical reactions.