ChemistryAtomsProperties of Protons, Neutrons, and ElectronsAtomic Number and WeightSlide 5IsotopesElectron ShellsIonsChemical BondsIonic BondsIonic Bonds, pt. 2Covalent BondsSingle, Double, and Triple BondsPolar Covalent BondsHydrogen BondsWaterSlide 17Slide 18Other Properties of WaterAcids and BasesSlide 21pH ScaleBuffers and SaltsSlide 24Slide 25Chemistry•At the bottom, biology is nothing but applied chemistry•All matter is composed of atoms•Elements such as carbon and oxygen are a group of atoms of the same type. For instance, a nail made of iron is just a large group of iron atoms.•There are 92 naturally occurring elements, plus about 25 artificially-created elements.•Living things are mainly composed of the elements carbon, hydrogen, oxygen, and nitrogen. Another dozen or so elements are also used: phosphorus, iron, magnesium, sodium, potassium, chlorine, to name a few.Atoms•Atoms have 3 components: protons, neutrons, and electrons•protons and neutrons are in the nucleus •Electrons circle around the nucleus•NOTE! This nucleus is NOT the same as the cell’s nucleusProperties of Protons, Neutrons, and Electrons•Protons have a mass of 1 unit. If you had 600,000,000,000,000,000,000,000 protons you would have 1 gram. Protons also have an electrical charge of +1: protons are positively charged.•Neutrons also have a mass of 1 unit. Most of the mass of any object is in its protons and neutrons. Neutrons are neutral (not electrically charged).•Electrons weigh about 1/2000 of a unit, very light. They have a -1 charge (negatively charged).Atomic Number and Weight•The atomic number of an atom is the number of protons it has. The atomic number defines the basic identity of the atom: what element it is. For example. All hydrogen atoms have 1 proton (atomic number = 1), ↑ and all carbon atoms have 6 protons (atomic number = 6). All gold atoms have 79 protons; uranium atoms have 92 protons. protonprotons neutronsAtomic Number and Weight•The atomic weight of an atom is the number of protons plus the number of neutrons. Most hydrogen atoms have 1 proton and no neutrons, so the atomic weight is 1. Most carbon atoms have 6 protons and 6 neutrons, so the atomic weight is 12.•Electrons are very light, so they don’t add significantly to the atomic weight.atomic weightIsotopes•Isotopes are atoms with the same atomic number (same element) but different atomic weights: that is, isotopes have the same number of protons but different numbers of neutrons.•Different isotopes of the same element all have the same chemical properties. Chemical properties are determined by the number of protons only.•Heavier isotopes (too many neutrons) are usually radioactive.Electron Shells•Atoms are usually neutral in electrical charge, which means that they have the same number of electrons (- charge) as protons (+ charge).•Electrons circle the nucleus at defined positions called shells.•The innermost shell of every atom holds 2 electrons (except hydrogen, which only has 1 electron).•All other shells hold up to 8 electrons•Electrons fill in from the nucleus out, so the inner shells are always full. •In most atoms, the outermost shell is not full.•Most chemistry is caused by the electrons of the outermost shell: atoms have a “desire” to have a full outer shell with 8 electrons in it.Ions•The number of electrons in an atom is usually the same as the number of protons. Since electrons have a -1 charge and protons have a +1 charge, atoms are electrically neutral.•Ions are atoms where the number of electrons is different from the number of protons.•Ions have an electrical charge: positive charge if more protons than electrons, and negative charge if more electrons than protons.•For example, sodium atoms have 11 protons. Neutral sodium atoms also have 11 electrons, but sodium ions have only 10 electrons: 11 protons plus 10 electrons, giving a total charge of +1.Chemical Bonds•Atoms can combine with each other to form molecules.•A molecule is a defined number of atoms grouped into a defined spatial relationship. For example, water, H2O, is 2 hydrogen atoms connected to an oxygen atom. The oxygen is in the middle, and the hydrogens are attached at an angle to it. •A large group of the same molecule is called a compound (just as a large group of the same atom is called an element).•Molecules are held together by chemical bonds.•Chemical bonds are the result of 2 forces:• 1. The octet rule, which means that atoms want to have 8 electrons in their outer shell (2 in the case of hydrogen).• 2. The attraction between atoms of opposite electrical charge.•The three main types of chemical bond are; ionic bond, covalent bond, and hydrogen bond.Ionic Bonds•In an ionic bond, one atom gives an electron to another atom. This makes both atoms ions, and they are held together because their opposite charges attract each other.↑ In sodium chloride (table salt), sodium starts out with 1 electron in its outer shell. The next shell down has 8 electrons, so by giving 1 electron away, the sodium atom gets a full outer shell. It then has a +1 charge.•Chlorine starts out with 7 electrons in its outer shell. By gaining one more electron, it gets 8 in the outer shell, and a -1 charge.↑ The + charged sodium and the – charged chlorine attract each other, and they pack together in salt crystals.Ionic Bonds, pt. 2•Na = sodium atom; Cl = chlorine atom (called chloride when in a compound).•NaCl = one sodium plus one chlorine combined into a compound, sodium chloride (table salt).•The properties of sodium chloride are very different from sodium, a soft flammable metal, and chlorine, a poisonous gas.•Ionic bonds are very strong, but they are easily broken by water.Covalent Bonds•Covalent bonds occur when 2 atoms share a pair of electrons. The electrons spend part of their time with both atoms, so the octet rule is satisfied sufficiently.•A molecule of hydrogen gas, H2, has 2 hydrogen atoms. Each atom provides 1 electron, so in the bond each atom shares 2, a complete shell for hydrogen.•The bond is symbolized as a line connecting the 2 H’s: H-H↑ In water (H2O), the oxygen has 6 electrons in its outer shell, and it shares one with each of the 2 hydrogens, giving 8 shared electrons for oxygen and 2 for each hydrogen. •Covalent bonds are the most common type in biological molecules.Single, Double, and Triple Bonds•In a single