What is Matter? Matter is any substance in the universe that has mass and occupies space All matter is composed of extremely small particles called atoms Every atom has the same basic structure –Core nucleus of protons and neutrons –Orbiting cloud of electrons

More Models of Atoms Note electron cloud

Look at the samples at the front desk Element –A substance that cannot be broken down by ordinary chemical means (one type of atom) Does anyone know the chemical symbol for these? Iron, Oxygen and Hydrogen Where can we find this information?

1 H C What do these numbers stand for? What kind of information can we get from the periodic table?

Chemical Formulas The chemical formula of a substance indicates: –The elements in the molecule –The number of atoms of each element in the substance Example:6H 2 S0 4 –2 atoms of the element hydrogen; 1 atom of the element sulfur; 4 atoms of the element oxygen A number in front of substance indicates how many molecules of that substance there are: –There are 6 molecules of H 2 S0 4 in the example

Electron shells Atomic number = number of protons = number of electrons for element Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. Electron shells determine how an atom behaves when it encounters other atoms

Electrons Each electron shell has a specific # of orbitals –First orbital holds up to two electrons Fig. 3.3 Atoms with incomplete electron orbitals are more reactive

Stability Atoms will react to maintain 8 electrons in their valence shell (except the first shell which is full at 2 electrons) If valence shell has less than 8 electrons the atom will gain, lose or share electrons to remain STABLE.

Question: Do you feel good when you and your friend share things? How would you feel if your friend gave you something to make you happy? ml

Types of Chemical Bonds The Major Chemical Bonds of Biomolecules: –Ionic Bond –Covalent Bond Non-Polar Polar -Hydrogen bond

Ionic Bond – Sodium chloride Sodium tends to give up its single electron in its valence shell Chlorine pick up one electron to completely fill its valence shell

Ionic Bonds Formed when electrons are completely transferred from one atom to another During bonding, atoms gain or lose electrons Now called ions: negatively or positively charged What do we know about + and -? Examples; NaCl, CaCl 2, K 2 O

Covalent Bond Between nonmetallic elements of similar electronegativity Formed by sharing electron pairs Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC 2 types: - Nonpolar and Polar

when electrons are shared equally NONPOLAR COVALENT BONDS H 2 or Cl 2

Polar Covalent Bonds: Unevenly matched, but willing to share.

when electrons are shared but shared unequally POLAR COVALENT BONDS H2OH2O

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Electronegativity Is a chemical property that is a measure of the tendency of an atom to attract a bonding pair of electrons. (Wikipedia and Decreases down a group Increases with increasing atomic number going across a period Which is more electronegative? S or Fl, C or O, Mg or P

Put your knowledge to work Why is H 2 S a gas and H 2 O a liquid at room temperature? Write a response based on the chemistry information you have.

Hydrogen Bonds Attraction between partially (-) and partially (+) charged atoms Examples: Exist between adjacent water molecules Between polarized regions of same large molecules (protein) Between 2 strands of a DNA molecule

Take out a piece of paper 1.What are the types of bonding? 2.What makes each bond different from the others? 3.Give an example of each bond. 4.Hand in at the end of the period