Introduction to Chemistry Lecture #11 Honors Biology Ms. Day

Composition of Matter Matter - everything in universe is composed of matter (“stuff”) Matter is anything that occupies space or has mass Mass – quantity of matter an object has Weight – pull of gravity on an object Volume – amount of space something takes up

Elements Pure substances that cannot be broken down Made of a single type of atom More than 100 elements (92 naturally occurring)

Atoms smallest piece of matter Can NOT be broken down Atom have 3 subparticles: Protons + charged particle Neutrons Neutral (0) charged particle Electrons - charged particle

The Nucleus Middle of the atom Holds positive charged protons and neutral neutrons (p’s + n’s) Positively charged Contains most of the mass of the atom p n

Protons All atoms of a given element have the same number of protons # of protons = also known as the atomic number # of protons (+’s) = # of electrons (-’s) If you change the PROTON #, you change the atom!!

Most Common Elements 90% of the mass of an organism is composed of 4 elements (carbon, oxygen, hydrogen and nitrogen  “COHN”) Each element unique chemical symbol Consists of 1-2 letters First letter is always capitalized

Neutrons The number varies slightly among atoms of the same element Different number of neutrons produces isotopes of the same element Neutron # = Mass # - # protons (atomic #)

Radioactive Isotopes Natural or artificially created isotope UNSTABLE Nucleus decays (breaks down) until stable Uses include: 1) kill or inhibit (stop) specific abnormal cells 2) treat abnormal cell growth 3) Radioactive tracers

Electrons Negatively charged high energy particles with little or no mass # electrons = # protons Travel at very high speeds in different energy levels Energy levels are different distances from the nucleus

Ions Ions are atoms that have EXTRA or MISSING electrons # electrons = # protons Examples: Na+ is MISSING 1 electron It has 1 extra positive charge (+) Ca+2 is MISSING 2 electrons It has 2 extra positive charges (+2) Cl- has 1 extra electron It has 1 extra negative charge (-)

Compounds Most atoms do not exist by themselves Atoms combined with other atoms to form compounds 2 types of compounds: 1) molecules 2) ionic (salts)

Compounds A compound is a pure substance made up of atoms of two or more elements Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound EX: C6H12O6 (glucose) or H20 (water)

Chemical Formulas 2H202  2H2O + O2 Subscript after a symbol tell the number of atoms of each element H20 has 2 atoms of hydrogen & 1 atom of oxygen Coefficients before a formula tell the number of molecules 3O2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen

Bonds Molecular “glue” Holds atoms together to form compounds Valence (outermost) electrons are involved in bonding

Bonds Single Double Triple Bonds SIZE decreases as you increase # of bonds Bonds STRENGTH increases as you increase # of bonds

Types of Bonds: 1) Covalent Bonds Formed when two atoms share one or more pairs of electrons in a compound “Co” means “together” Found in molecules Ex: water

Types of Bonds: 2) Ionic Bonds Bond involves the electrical attraction between oppositely charged ions (+ and -) Some atoms become stable by losing or gaining electrons Atoms that lose electrons are called positive ions (Ex: Na+) A.k.a= a cation Atoms that gain electrons are called negative ions (Ex: Cl-) A.k.a= an anion

Ionic Bonds (Con’t) Because positive and negative electrical charges attract each other ionic bonds form

Covalent vs. Ionic Bonds

Types of Bonds: 3) Hydrogen Bonds An attraction between a hydrogen (H) atom and another atom (usually O, N or F) Found between molecules Ex: water or in middle of DNA

Bonds vs. Strength Covalent bonds are the STRONGEST! Hydrogen bonds are the WEAKEST!

States of Matter Atoms are in constant motion (called kinetic energy) The rate at which atoms or molecules in a substance move determines its state