The document discusses the structure of atoms. It defines an atom as the smallest particle of an element that retains its identity in chemical reactions. It describes how atoms are composed of subatomic particles including protons, neutrons, and electrons. It discusses how the number of protons determines the element, the number of electrons usually equals the number of protons, and the mass number is the total of protons and neutrons. Isotopes are defined as atoms of the same element with different numbers of neutrons. The document also discusses electron shells and valence electrons.

1. Atomic Structure

2. The atom Def: the smallest particle of an element that retains its identity in a chemical reaction. Atoms are tiny! If you lined up 100,000,000 copper atoms side by side, they would produce a line only 1 cm long.

3. Initial Thoughts Democritus – atoms are indivisible and indestructible Dalton modified this theory through research. He determined that: 1.elements are composed of tiny indivisible particles called atoms 2.atoms of the same element are identical 3.atoms can combine to form compounds 4.chemical reactions occur when atoms are separated from their compounds Thompson was the first to discover that atoms contain subatomic particles

4. Subatomic Particles Particle Location Charge Mass Proton (p + ) 1.67 x 10 -28 g Neutron (n o ) 1.67 x 10 -28 g Electron (e - ) negligible

5. Using the Periodic Table How do I determine the number of protons? How do I determine the number of electrons? How do I determine the mass number? How do I determine the number of neutrons? Practice on your own

6. Isotopes Isotopes of an element have the same number of protons but different number of neutrons Ex: Lithium -7 and Lithium-6 Draw Bohr models of Carbon-12 and Carbon-13 Why does mass number (protons + neutrons) differ from atomic mass (the number you find on the periodic table)? (pg 114)

7. Electrons According to the discovery Bohr made, electrons are found in orbitals (or energy levels) surrounding the nucleus 1 st energy level – can hold 2 electrons 2 nd energy level– can hold 8 electrons 3 rd energy level – can hold 18 electrons

8. Valence Electrons The number of valence electrons can be determined by looking at the Roman Numeral at the top of each group (or family) or the periodic table. The number of valence electrons can give us hints about the reactivity of that element Metals lose valence electrons to form cations Non-metals gain valence electrons to form anions Pg 162

9. Rutherford’s Gold Foil Experiment Proposed that: the atom is mostly empty space the nucleus is concentrated in the center of the atom Think of a dime in the middle of football field Demo 1

10. In-class assessment You have the next 2o-25 minutes to complete an open notebook quiz.

11. HW Section 4.1 review worksheet – due Thursday Section 4.2 review worksheet – due Friday