Atoms and Molecules Caffeine molecule Macromolecule –a Protein

Atomic structure Small, dense nucleus –Protons: (+) charge –Neutrons : (0) no charge Electrons (-) found in orbitals of different energy levels around the nucleus.Electrons (-) found in orbitals of different energy levels around the nucleus. # Protons = # electrons Electrically neutral, as + and – charges are equal

Energy levels Electrons fill up orbitals around the nucleus from the inside out. Each level holds only so many electrons Level 1- holds 2 Level 2 – holds 8 Level 3- holds 8

Valence electrons the electrons on the outermost level are called valence electrons, and they determine reactivitythe electrons on the outermost level are called valence electrons, and they determine reactivity Reactivity is how likely an atom is to form bonds with another elementReactivity is how likely an atom is to form bonds with another element Think: How many valence electrons does Ar have? and H?

Elements Every element has a unique number of protons. –It is the number of protons that defines what the element is. –The atomic number is the number of protons –The atomic mass is the number of protons plus neutrons Lithium: Atomic # = 3, Atomic mass = 6

The periodic table The periodic table is a tool that organizes elements –Groups (columns). of elements have the same number of valence electrons –Periods (rows) of elements have the same number of energy levels.

What is a chemical bond? Attractive forces that hold atoms and ions together, making molecules An ionic bond holds ions together A covalent bond holds atoms together

Types of bonds Covalent bondsCovalent bonds –Two or more atoms share electrons. –Example: water Ionic bondsIonic bonds –Formed when electrons are transferred. –Atoms become charged (ions) –Opposite charged ions attract each other. –Example: salt Water: two hydrogen atoms plus an oxygen atom. Salt: one chlorine atom plus one sodium atom.

Compounds Molecules composed of atoms of two or more elements.Molecules composed of atoms of two or more elements. Held together by chemical bonds.Held together by chemical bonds. –Chemical bonds require energy to form. –Chemical bonds result from outer electrons (valence electrons) interacting. Methane gas molecule CH 4 Think: How many atoms are in methane? How many elements are in methane?

Polarity Elections are either shared equally or not between atoms in a compounds Polar: When electrons are not shared equally, one end of the molecule is more positive and the other more negative. Nonpolar: an even distribution of charge

Summary: answer the following as a 7 sentence paragraph 1.What is the basic structure of an atom? 2.What is an element? 3.Why do elements form bonds? 4.What type of bonds do elements form? 5.What is a compound? 6.What is polarity?