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?

Atom: basic unit of matter 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? All elements and info about them can be found on….

Element name Atomic Number Element Symbol Atomic Mass

Atomic Number and Atomic mass Number of protons in that element Neutral atoms also have that same number of electrons Atomic mass Mass of protons and neutrons

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… but what we really care about is the outer most shell.. The valence shell. This determines reactivity. DRAW CARBON BOHR’S.

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 element The closer to stable, the more reactive If the shell is full, the atom is non-reactive Noble gases Is carbon stable? NO… how many valence electrons?

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

Unstable Atoms “like” to become stable Ions Ionic bonds Covalent bonds Ions (cation/anion for honors) Ionic example: sodium chloride (on hw page) Covalent: water

Practice Draw a sodium atom How many valence electrons does it have? What does that say about its reactivity? Draw a sodium ion

Today 8/23 Review ions Atoms that have gained/lost electrons Example: sodium ion Learn about ionic bonding Example: lithium chloride covalent bonding Example: water, Honors: S2, N2 practice

Ionic Bonds Attraction between oppositely charged ions

Covalent Bonds Sharing of valence electrons