Do Now: How do I decide if I should use a line graph or a bar graph? What does my cat and a positive ion have in common?

Graphing: Spot the Errors! Students should note:  Missing axis  label, units for temperature, scale is not consistent, Title should be more descriptive.  Connect the dots for continuous data.

2.3 Atoms can bond together to form molecules or compounds. When you eat a meal, it is like filling your car’s tank up with gasoline; you have a source of energy that can be used to fuel activities like running, thinking, building muscle, and maintaining the machinery of life. Energy is stored in bonds that join atoms together. Eventually the bonds are broken, the energy is released, and it can be used to fuel the body’s activities.

Molecules Products of bonding! Groups of atoms held together by bonds are called molecules. It takes a certain amount of energy to break a bond between two atoms. The amount of this energy, called the bond energy, depends on the atoms involved. In a sense, the molecules are created as short-term storage of energy that can be harnessed later.

Before looking at specific types of bonds that hold molecules together, let’s look at how molecules are illustrated. In this book you will most often see molecular structures represented by the ball-and-stick and space-filling models. Lewis Model – shown by element symbol and lines that represent bonds Ball-and-stick – ball = atom, stick = bonds Space filling model = similar to ball and stick but each sphere surface is adjacent to other spheres

3 types of bonds Covalent Ionic Hydrogen There are three principal types of bonds that hold multiple atoms together. Type of bond dependents on characteristics of atom, and in particular the structure of the outer shell where valence electrons are.

Covalent Bonds Insert fig 2-9 to right side of slide Covalent bonds are strong bonds formed when two atoms share electrons. The simplest example of a covalent bond is the bonding of two hydrogen atoms to form H2. Because the atom is most stable when the first shell has two electrons, two hydrogen atoms can each achieve a complete outermost shell by sharing electrons. The sharing of two electrons among two atoms is called a double bond. Practice covalent bonding. Draw a bohr model of a oxygen atom. How many electrons are in its outer shell? 6 – so it needs 2 to fill its outer shell. 2 hydrogen atoms can each share one electron. Usually between two non metals

Ions and Ionic Bonds Insert fig 2-10 Atoms can also bond together without sharing electrons. When one atom transfers one or more of its electrons completely to another, each atom becomes an ion, since each has an unequal number of protons and electrons. The atom gaining electrons becomes negatively charged, while the atom losing electrons becomes positively charged. Usually between a metal and non-metal An ionic bond occurs when the two oppositely charged ions attract each other and form a compound, a molecule made up of two or more elements. Ionic bonds are generally similar in strength to covalent bonds. Unlike covalent bonds, in ionic bonds each electron circles around a single nucleus. Ions of equal and opposite charges are attracted to each other and the compound is neutral—that is, it has no charge (Fig. 2-10).

Metal or Non-metal?

Hydrogen Bonds Insert fig 2-11 Ionic and covalent bonds link two or more atoms together. Hydrogen bonds, on the other hand, are important in bonding multi-atom molecules together. A hydrogen bond is formed between a hydrogen in one molecule and another molecule, often an oxygen or nitrogen atom. This bond is based on the attraction between positive and negative charges. These atoms are not ions, so where do the electrical charges come from? The hydrogen atom is already covalently bonded to another atom within the same molecule and shares its electron. That electron will circle both the hydrogen nucleus and the nucleus of the other atom, but the electron is not shared equally. Given that the other atom will always have more than the one proton found in the hydrogen nucleus, the hydrogen electron spends more of its time near the other, more positively charged nucleus than its own nucleus. Having an extra electron nearby causes the larger atom to be slightly negatively charged, while the hydrogen atom becomes slightly positively charged. In a sense, the covalently bonded molecules become like a magnet, with distinct positive and negative sides. Magnet-like molecules with distinct positive and negative regions like this are called polar.

Types of Bonds Covalent Ionic Hydrogen Bond Strength: Students should build GO on their own and then share out. Covalent:  Strong bonds, electrons are shared, circle both nuclei; between two non-metals  Ionic:  Strong bonds, electrons are donated/transferred/received, circle only one nucleus, between metal and non-metal;   Hydrogen:  weak bond, Hydrogen atom of molecule is slightly positive and attracted to slightly negative atom of another molecule

Insert fig 2-12 Figure 2-12 A review of the three types of bonds discussed in this section.