Atomic Bonds FIRST: Pass up your homework “exit ticket” THEN: Classify the following as elements, compounds, atoms, or molecules 1.A gold (Au) nugget 2.The smallest piece of water (H 2 O) possible. 3.A glass window (SiO 2 ) 4.The smallest piece of sodium (Na) possible

Answers A gold nugget is an element, since it is made of many gold atoms (and only gold atoms!) The smallest piece of water is a single water molecule. Any smaller than that, and it’s not water! SiO 2 (glass) is a compound, since it is made up of several types of atoms joined together. [note: the smallest piece of glass possible would be a single molecule of SiO2] Since sodium (Na) is an element, the smallest sample possible is a single sodium atom.

Atomic Bonds [aka chemical bonds] What is a bond? So what is an atomic bond? An attractive force between 2 atoms.

Please Copy the following chart into your notes: Type of bondWhat happensExample molecule

What causes atomic bonds? When atoms change how they are bonded to one another, that is called a chemical reaction. Why do chemical reactions happen?

What’s more likely? Things go from high energy to low! Water flowing down a cliff to make a waterfall… or water flowing up? Falling down a flight of stairs or falling up? Dropping an egg and making a mess or dropping a broken egg and getting one that’s back together?

It’s all about Potential Energy Atoms bond to get a lower energy configuration. Arrows indicate increasing potential energy

But Why? ELECTRONS DETERMINE HOW ATOMS BOND Atoms that have a full outer energy level are very stable. This is the driving force of bonding reactions. Atoms bond together in a way that fills their outermost electron energy level. (2 or 8) This is the lowest energy configuration possible.

Ionic Bonds An atom loses 1 or more valence electrons, giving it a positive charge. Another atom gains the electron(s) and becomes negatively charged + & - ions attract. Na Cl e- - +

Covalent bonds 2 atoms share a pair of valence electrons H e- H

It’s all about Energy Ne 2-7 Not Stable 2-8 VERY Stable Not Stable

TWIST: Polar Covalent Bonds In a polar covalent bond, a pair of electrons is shared between two atoms… unevenly One part of the molecule now has a small – charge, and the other has a small + charge Electron Sharing 100% Non-polar covalent Polar covalent 100% Ionic

What types of bonds atoms form Almost always lose electrons Don’t bond Almost always gain electrons Polar (greedy for electrons) Mostly non-polar Metals (electrons “float” around nuclei) + -

To the Video! HOMEWORK: Read 2-1, answer SR #1,2,4

Modeling Atomic Bonds Work in a group of NO MORE THAN 3, and explore the foam board bonding models. As you do so, complete the worksheet you picked up.