Transcript Chapter 3
Chapter 3 Chemistry 3.1 Matter • Matter – anything that occupies space and has mass • Mass is the quantity of matter an object has • The pull of gravity on an objects mass gives it weight • Changes in matter are essential to life’s processes Physical Properties of Matter • Can be observed or measured without permanently changing the identify of the matter • Ex. - Color, odor, texture, taste, hardness, melting point, boiling point Chemical Properties of Matter • Describes the ability to change into a new substance as a result of a chemical change • Ex. Coal burning – can not get it back 3.2 Atoms • Fundamental unit of matter (atom) • Atoms are the basic building blocks of matter • Cannot be subdivided further by any ordinary chemical means • Made up of subatomic particles (P, N, E) • Have a net zero charge Structure of Atoms • Nucleus – small central part – made of protons and neutrons • Protons – positively charged particles • Neutrons – neutral particles • Electrons – negatively charged particles found in the space outside the nucleus The Nucleus • Atomic number – the number of protons in the nucleus determines the atomic number of an element • Each atom has it’s own atomic number • Most of the mass of an atom lies in its nucleus • Mass number – the mass of the entire atom is equal to the sum of its protons and neutrons • Mass number – atomic number = # of N • Atomic Mass – the average mass of all of the atoms of a particular element Electrons • Atoms generally have the same number of protons and electrons • Atoms are electrically neutral in normal circumstances • Electrons determine the chemical properties of atoms • Electrons are arranged in levels – energy levels Energy Levels • Each energy level is a different distance from the nucleus • The first energy level holds 2 e• The second energy level holds 8 e- • A filled outer energy level is a stable electron arrangement • Atoms with unfilled energy levels (valence shells) tend to form compounds where each atom has a filled outer level • Gain, lose or share • First Energy Level: 2 Second Energy Level: 8 Third Energy Level: 18 Fourth Energy Level: 18 Fifth Energy Level: 8 Elements • Made of only one type of atom • Cannot be broken down into simpler substances • Ex. O2, Fe2 Compounds • Made when two or more kinds of atoms are combined in definite proportions • Differs in physical and chemical properties from the elements that compose it • Can be separated into the elements that make them up • Ex. CO2, H2O Chemical Formula • Shows the kind and proportion of atoms that form a particular compound • Ex. CO2, H2O Structural Formula • Shows the number and kind of atoms in a molecule but also how the atoms are bonded to one another Isotopes • Varieties of an element that differ only in the number of neutrons • Not exactly alike but they behave the same way chemically – same number of e• Ex. Hydrogen – Protium, Deuterium, Tritium Radioactive Isotopes • The nuclei of many isotopes are unstable • Radioactivity – unstable nuclei give off (emit) charged particles and radiation • Loss of particles (protons) changes the particle to different isotopes, usually of a different element Practical Uses of Radioactive Isotopes • Tracer – can follow the isotope through stages in a chemical reaction – – – – – Ex. P-32 – plants I – 131 – Thyroid gland Fe – 59 – blood circulation Cobalt 60 – used to kill cancer cells Carbon 14 – brain tumor • Kill bacteria that cause food to spoil • Measure the age of certain rocks • Must be careful – radiation can kill 3-3 Interactions of Matter • Chemical bonding – combining of atoms of elements • Atoms follow rules • Rules are based on the number of e- in the outer energy level Ionic Bonds • Transfer of e- from one atom to another • Caused from the gain or loss of electrons • Ion – charged particle Na+ Cl• Formed when an ionic bond occurs • Ex. NaCl Covalent Bonds • Sharing of e• Shared e- are in the outer most level of both atoms at the same time • Strong bond • Single, double or triple • Ex. CO2, H2O, Br2, F2 • H-H, O=O, N N Molecule • Formed when 2 or more atoms join together in a covalent bond • Ex. CO2, H2O, NH3, C6H12O6 • Regardless of the type of bond formed atoms change their physical and chemical properties when they form a compound Ex. Na – silvery metal, reacts explosively with water Cl – poisonous greenish gas – WWI NaCl – table salt – solid- dissolves in water – not poisonous 3.4 Chemical Reaction Reactants products AgNO3 and NaCl AgCl3(s) + NaNO3 Hydrogen Gas Reacting with Oxygen Chemical Equation O2 + 2H2 (yields) 2H2O 2H2O O2 +2H2 (Does not happen. Why?) Balancing Equations • Chemists have learned that the most important factor in determining whether a reaction will occur is the flow of energy. • Spontaneous reactions release energy. The End