Atoms and Molecules The stuff life is made of.

Atoms Crucial points: An atom is the smallest unit of an element. Atoms are made up of electrons, protons, and neutrons. Electrons orbit in energy shells (also called valence shells). The electrons in the outer shell are most important to forming bonds between atoms.

An atom is the smallest unit of an element. Each element has distinct properties (color, melting point, reactivity, etc.) Properties arise from the basic atomic structure of each element.

Atoms are made up of sub- atomic particles. Electrons Protons Neutrons

Electrons orbit in energy (valence) shells

Bonding: Ionic Ionic bonds involve the transfer of electrons from one atom to another. Ionic bonds are strong bonds. Ionically-bonded atoms tend to form crystaline structures rather than individual molecules. Ionically-bonded substances tend to be soluble in water.

Bonding: Ionic

Why are these called ionic bonds? When an atom has the same number of electrons as protons, it is electrically neutral but… When an atom has one more electron than protons, it has a negative charge. If it has one less electron than protons, it has a positive charge. Atoms with an electrical charge are called ions.

Isotopes Isotopes are also different forms of the same atom. Different isotopes have the same number of protons and electrons, but different numbers of neutrons.

Bonding: Covalent Covalent bonds involve sharing of electrons between atoms. Covalent bonds result in individual molecules. Covalent bonds may be: Neutral Polar

Bonds: Covalent Two hydrogen atoms share electrons, forming a covalent bond

Bonds: Covalent In a water molecule, the oxygen atom tends to keep the shared electrons longer than the hydrogen atoms, creating a polar covalent bond

Bonds: Hydrogen Hydrogen bonds are weak bonds that form and break easily. Hydrogen bonds link molecules together. Hydrogen bonds are electrical attractions between polar molecules.

Bonding: Hydrogen Here, water molecules form hydrogen bonds with one another. The positive end of one molecule is attracted to the negative end of the next.

Bonding: Hydrogen Here, sugar molecules (polar) are in a solution with water (also polar). Where would hydrogen bonds form?

Recap Atoms are the basic units of an element. Atoms bond together to form molecules. Ionic bonds are electrical attractions between ions. Covalent bonds involve sharing of electrons between atoms. Covalent bonds form discreet molecules. Hydrogen bonds link molecules together.