Protons & Valence Protons & Valence ElectronsElectrons

8.5B: Identify that protons determine an 8.5B: Identify that protons determine an element’s identity, valence electrons element’s identity, valence electrons

determine its chemical properties, including determine its chemical properties, including reactivityreactivity

ProtonsProtonsProtons are positively-charged, Protons are positively-charged, subatomic particles found in the subatomic particles found in the nucleus of an atom. They contribute to nucleus of an atom. They contribute to the mass of an atom. They ARE the the mass of an atom. They ARE the IDENTITY of the atom. IDENTITY of the atom. The number of The number of protons does not changeprotons does not change..

The atomic number IS the number of protons

An atom with 8 protons is ALWAYS Oxygen

Protons are the Identity Protons are the Identity of Atomsof AtomsEach element has a unique number of Each element has a unique number of protonsprotons in in

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

Valence ElectronsValence ElectronsValence electrons are the electrons in Valence electrons are the electrons in the outermost energy level or orbital. the outermost energy level or orbital. They determine an atom’s reactivity.They determine an atom’s reactivity.

This Carbon atom has four valence electrons.

ReactivityReactivityReactivity is the rate at which a chemical Reactivity is the rate at which a chemical substance tends to undergo a chemical substance tends to undergo a chemical reaction (bond with other atoms)reaction (bond with other atoms)

Lithium reacting with waterLithium reacting with water

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