Journal #20 1. Who discovered the electron? 2. What did Rutherford discover?

Learning Goal: Today, we will identify the number of protons, neutrons and electrons for a given element.

Atoms Elements consist of atoms. An atom is the smallest unit of an element that has the chemical properties of that element.

Atomic Structure Even though elements are very tiny, they are made up of smaller parts called subatomic particles. There are 3 kinds of subatomic particles: Protons- positive charge Neutrons-no charge Electrons-negative charge

The Nucleus The nucleus is the small region in the center of an atom. The nucleus has a positive charge because it contains only protons and neutrons.

The Electron Cloud Electrons move around the nucleus in a space called the electron cloud.

Atomic Number The atomic number is equal to the number of protons in an atom. Example: Carbon has an atomic number of 6. That means it has 6 protons Elements on the periodic table are ordered according to their atomic number.

Number of electrons For all neutrally charged elements, the number of protons equals the number of electrons: Example: Oxygen has an atomic number of 8. 8 protons 8 electrons

Atomic Mass The atomic mass is equal to # of protons + # neutrons. Example: Carbon has an atomic mass of 12 and an atomic number of 6. Therefore : 12(mass)-6(protons)= 6 neutrons

Isotopes Although all atoms of a given element contain the same number of protons, the number of neutrons may differ. Isotopes are named according to their atomic mass Example: Most helium atoms have 2 neutrons, some helium atoms only have one neutron.

Let’s Practice: 1. For the element Oxygen: identify the number of protons, neutrons and electrons. 2. For the element Carbon-13: identify the number of protons, neutrons and electrons 3. For the element Hydrogen- identify the number of protons, neutrons and electrons