2/23/12 - Bellringer Explain and draw what you think a water molecule looks like.

Chapter 22 – Chemical Bonds 22.1 – Stability in bonding

Objectives Describe how a compound differs from its component elements. Explain what a chemical formula represents. Discuss why chemical bonding occurs.

Compounds When elements chemically combine Often have chemical and physical properties that aren’t anything like those of the individual elements

NaCl = Table Salt How different… Na = shiny, soft metal that reacts violently with water Cl = poisonous greenish yellow gas How different… Physically? Chemically? http://www.youtube.com/watch?v=9bAhCHedVB4

Chemical Formula Tells what elements a compound contains and the exact number of the atoms of each element in a unit of that compound H2O 2 Hydrogen atoms and 1 oxygen atom in every unit of water Subscript = written below Superscript = written above

Chemistry Jokes Two chemists went into a bar. Why? Chemist 1 asked for some H2O Chemist 2 asked for some H2O too… and died horribly. Why?

Atomic Stability Atoms form compounds because electric forces between electrons and protons attract and hold atoms and molecules together

Noble gases Unusually stable 8 outer electrons = full valence shell Atoms are stable when they have a full valence shell Elements get full shells by forming compounds Gain, lose, or share electrons

Electrons and Energy Levels Period tells you how many energy levels the element has

How do elements fill outer energy levels? They do this by combining with other atoms that also have partially complete outer energy levels. As a result, each achieves stability. Group 1 and 17 (7A) atoms combine easily. Why?

This illustration shows electron dot diagrams for sodium and chlorine. When they combine, sodium loses one electron and chlorine gains one electron.

Sodium had only one electron in its outer energy level, which is lost to combine with chlorine in sodium chloride. It drops down to a new outer energy level, and it is stable with eight electrons.

When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound. This attraction is called a chemical bond. A chemical bond is the force that holds atoms together in a compound.

In-Class Assignment/Homework 22.1 WKT

Plan 22.1 notes Lewis Dot Diagrams notes 22.2 notes 22.3 notes 22.1 WS Practice sheet (non-compound) 22.2 notes Dating game Lewis Dot compound practice sheet 22.3 notes Bond with a classmate