1 A Bonding Experience

2 Why atoms combine Atoms combine together to form molecules and compounds Why do atoms form molecules/compounds? An incomplete valence shell is unstable, so… Atoms with incomplete valence shells can interact with certain other atoms in order to complete its valence shell

3 Filling the Valence Shell In order to complete its valence shell, an atom can do one of two things: Share electrons with the other atom Share electrons with the other atom Transfer electrons with the other atom Transfer electrons with the other atom These interactions usually result in an attraction between the involved atoms, causing them to stay close together This attraction is a chemical bond

4 Sharing electrons Two atoms, typically nonmetals, sharing their valence electrons with each other is called a covalent bond Each hydrogen atom is held in 1s orbital by its attraction to proton in nucleus. As two hydrogen atoms approach each other, the electron of each atom is also attracted to the other atom’s proton. The two electrons become shared in a covalent bond, forming an H 2 molecule.

5 A molecule is born Two or more atoms held together by a covalent bond is a molecule A single covalent bond (a pair of shared electrons) is single bond The single bond in a hydrogen molecule is represented by H—H and is called the structural formula ( H 2 is the molecular formula) A hydrogen molecule, H—H, where the “—” represents a single bond, the sharing of a single pair of electrons.

6 Another example Unlike hydrogen, an oxygen atom has 6 valence electrons O O O OOO How many pairs of electrons are shared between the oxygen atoms? Since there are two pairs of shared electrons, this is a double bond.

7 Why H 2 O? Both H 2 and O 2 are pure elements, not compounds We have seen what happens when hydrogen and oxygen combine: H 2 O We have seen that H and O always combine in a definite ratio of 2 hydrogen atoms for every 1 oxygen atom. But why???

8 When H and O meet H H O H H O HH O Since each hydrogen has 1 electron that it can share, it takes 2 hydrogen atoms sharing with oxygen in order to complete its valence shell. Each hydrogen atom completes its valence shell (only 2 electrons needed) because oxygen shares 1 electron with each hydrogen. If only I had 2 more electrons… It sure would be nice to share my electron with somebody… Yup.