Daily Science Label the following as a molecule, atom, compound, or both (molecule and compound) H3 H2O Ca NaCl How many and what kind of atoms do you see here: KMnO4

Chemical Bonds Biology 1

Chemical Bonds Atoms in molecules and compounds are held together by chemical bonds. Valence electrons are the electrons that form bonds. There are two main types of bonds: Ionic Covalent Hydrogen Atoms Bonding

Chemical Bonds Ionic Bonds – form when one or more valence electrons are transferred from one atom to another. (Metal + Nonmetal) Ion – an atom that has a charge because it has either lost or gained electrons. If an atom loses electrons, what is its charge? Positive If an atom gains electrons, what is its charge? Negative Positively charged ions are called cations. Negatively charged ions are called anions.

Each resulting ion has a completed valence shell Fig. 2-14-2 Ionic Bonding Na Na Cl Na Cl Na Cl Na+ Cl– Sodium atom Chlorine atom Sodium ion (a cation) Chloride ion (an anion) Figure 2.14 Electron transfer and ionic bonding Sodium chloride (NaCl) Each resulting ion has a completed valence shell 5

Draw this Staircase!

Metals and Nonmetals Metals are to the left of the staircase on the periodic table Ex: Iron (Fe), Cobalt (Co), Lithium (Li) Nonmetals are to the right of the staircase on the periodic table Ex: Carbon (C), Neon (Ne), Hydrogen (H)

Chemical Bonds Covalent Bonds – form when electrons are shared between two atoms. Valence electrons travel in the valence shell of both atoms. Electrons must be shared in pairs (one from each atom). Two electrons  Single Covalent Bond Four electrons  Double Covalent Bond Six electrons  Triple Covalent Bond

Covalent Bonding in Four Molecules Fig. 2-12 Name and Molecular Formula Electron- distribution Diagram Lewis Dot Structure and Structural Formula Space- filling Model Covalent Bonding in Four Molecules (a) Hydrogen (H2) (b) Oxygen (O2) (c) Water (H2O) Figure 2.12 Covalent bonding in four molecules (d) Methane (CH4) 9

Ionic and Covalent Bonds Video Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 10

Chemical Bonds Why do bonds form? Atoms want to have full valence shells. Having a full valence shell makes an atom inert (unreactive). Atoms will lose/gain/share electrons until their valence shell is full. The closer a valence shell is to being full, the more reactive an atom is. Check out this video!