Chemistry of Life Chapter 2

Warm Up 8/22 Try to recall the following information without referencing your textbook or a friend What is an atom? What is an element? What differentiates one element from another? What are protons, neutrons and electrons?

Answers Atom: basic unit of matter Element: a specific kind of atom Made up of 3 smaller particles Neutrons- no charge “neutral.” Found in nucleus Protons- positive charge. Found in nucleus Electrons- negative charge. Tiny. Orbit nucleus in a 3D “electron cloud” Element: a specific kind of atom Determined by number of PROTONS Examples?

In red you see the short cut that shows how many valence Electrons

Element name Atomic Number Element Symbol Atomic Mass

Atomic Number and Atomic mass Number of protons in that element (also equals the number of electrons) Atomic mass Mass of protons and neutrons *find the number of neutrons by: Atomic mass – atomic number

Bohr’s Atomic Model Nucleus in center (protons and neutrons) Electrons are in energy levels/energy shells surrounding the nucleus Energy level 1 holds up to 2 electrons Energy level 2 holds up to 8 electrons Energy level 3 holds up to 18 electrons There are 91 elements on the periodic table. 25 exist in living things. We will not go beyond 3rd energy level. 4 holds 32, then 50, then 72

Stability and Octet Rule An atom is stable if its outer shell is full OR has eight electrons (octet rule) The outer shell is known as the VALENCE shell The number of electrons in the valence shell determines the reactiveness of the the element The closer to stable, the more reactive If the shell is full, the atom is non-reactive Noble gases

Let’s draw some atoms *list the number of valence electrons for each Hydrogen Helium Oxygen Neon Magnesium

Unstable Atoms “like” to form bonds to become stable Ionic bonds Covalent bonds

Warm Up 8/21 Draw a fluorine atom How many valence electrons does it have? What does that say about its reactivity? Draw a fluorine ion

Today 8/22 Review ions Atoms that have gained/lost electrons Example: sodium ion Learn about ionic bonding Example: lithium chloride

Ionic Bonds Attraction between oppositely charged ions

Covalent Bonds Sharing of valence electrons Dogs teaching Chemistry