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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 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? What kind of information can we get from the periodic table? 1 H 1.0079 12 C 12.010 What do these numbers stand for? 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: 6H2S04 – 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 H2S04 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? http://www.coolcakesbylindsay.com/2012_07_01_archive.ht 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, CaCl2, K2O Covalent Bond • Between nonmetallic elements of similar electronegativity • Formed by sharing electron pairs • Examples; O2, CO2, C2H6, H2O, SiC • 2 types: - Nonpolar and Polar NONPOLAR COVALENT BONDS when electrons are shared equally H2 or Cl2 Polar Covalent Bonds: Unevenly matched, but willing to share. POLAR COVALENT BONDS when electrons are shared but shared unequally H2O - 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 www.chemguide.co.uk) • 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 H2S a gas and H2O 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