Slide 1 of 40 Copyright Pearson Prentice Hall Biology

Slide 2 of 40 Copyright Pearson Prentice Hall 2-1 The Nature of Matter

Slide 3 of 40 Copyright Pearson Prentice Hall Atoms *The study of chemistry begins with the basic unit of matter, the atom. The Greek philosopher Democritus called the smallest fragment of matter the atom, from the Greek word atomos.

2-1 The Nature of Matter Slide 4 of 40 Copyright Pearson Prentice Hall Atoms Atoms contain subatomic particles that are even smaller.

2-1 The Nature of Matter Slide 5 of 40 Copyright Pearson Prentice Hall Atoms What three subatomic particles make up atoms?

2-1 The Nature of Matter Slide 6 of 40 Copyright Pearson Prentice Hall Atoms The subatomic particles that make up atoms are Protons- (+) positive charge Neutrons- (0) no charge neutral Electrons- (-) negative charge

2-1 The Nature of Matter Slide 7 of 40 Copyright Pearson Prentice Hall Atoms The subatomic particles in a helium atom.

2-1 The Nature of Matter Slide 8 of 40 Copyright Pearson Prentice Hall Atoms Protons and neutrons are found in the nucleus or center of the atom. They are held together by strong forces. Protons & neutrons have about the same atomic mass, which is 1. *The atomic mass is the total number of protons & neutrons.

2-1 The Nature of Matter Slide 9 of 40 Copyright Pearson Prentice Hall Atoms * Electrons are in constant motion in the space surrounding the nucleus. *They have a negligible atomic mass (0). Electrons are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion.

2-1 The Nature of Matter Slide 10 of 40 Copyright Pearson Prentice Hall Atoms

2-1 The Nature of Matter Slide 11 of 40 Copyright Pearson Prentice Hall Atoms *Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutral. *protons (+) = electrons (-) If an atom has a charge it is called an Ion. * + ion- protons > electrons * - ion- protons< electrons

2-1 The Nature of Matter Slide 12 of 40 Copyright Pearson Prentice Hall Elements and Isotopes A chemical element is a pure substance that consists entirely of one type of atom. *Elements are represented by a one- or two-letter symbol. Ex: C stands for carbon. Ex: Na stands for sodium.

2-1 The Nature of Matter Slide 13 of 40 Copyright Pearson Prentice Hall Elements and Isotopes *The number of protons in an atom of an element is the element's atomic number (symbol Z). Carbon has 6 protons, so its atomic number is 6. *Every element has its own atomic number so it identifies the element. More than 100 elements are known, but only about two dozen are commonly found in living organisms.

2-1 The Nature of Matter Slide 14 of 40 Rules: 1.To find Protons, it is the same as the atomic number. 2.Protons = Electrons 3.To find Neutrons: atomic mass – atomic number Copyright Pearson Prentice Hall

2-1 The Nature of Matter Slide 15 of 40 *Periodic Table – list of all the elements Symbols- for the names of the elements Atomic numbers Atomic mass 6 atomic number C symbol atomic mass Copyright Pearson Prentice Hall

2-1 The Nature of Matter Slide 16 of 40 Copyright Pearson Prentice Hall Elements and Isotopes Isotopes Def: Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.

2-1 The Nature of Matter Slide 17 of 40 Copyright Pearson Prentice Hall Elements and Isotopes *Isotopes are identified by their mass numbers. For example, carbon has three isotopes—carbon-12, carbon-13, and carbon-14. Each isotope has a different number of neutrons.

2-1 The Nature of Matter Slide 18 of 40 Copyright Pearson Prentice Hall Elements and Isotopes How are all of the isotopes of an element similar?

2-1 The Nature of Matter Slide 19 of 40 Copyright Pearson Prentice Hall Elements and Isotopes Because they have the same number of electrons, all isotopes of an element have the same chemical properties.

2-1 The Nature of Matter Slide 20 of 40 Copyright Pearson Prentice Hall Elements and Isotopes Isotopes of Carbon 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 7 neutrons 6 electrons 6 protons 8 neutrons

2-1 The Nature of Matter Slide 21 of 40 Copyright Pearson Prentice Hall Elements and Isotopes Radioactive Isotopes Def: Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time. Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses.

2-1 The Nature of Matter Slide 22 of 40 Copyright Pearson Prentice Hall Elements and Isotopes *Radioactive isotopes can be used: to determine the ages of rocks and fossils. to treat cancer. to kill bacteria that cause food to spoil. as labels or “tracers” to follow the movement of substances within an organism.

2-1 The Nature of Matter Slide 23 of 40 Copyright Pearson Prentice Hall Chemical Compounds In nature, most elements are found combined with other elements in compounds. Def: A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. *The physical and chemical properties of a compound are different from the elements from which it is formed.

2-1 The Nature of Matter Slide 24 of 40 Copyright Pearson Prentice Hall Chemical Compounds *Scientists show the composition of compounds by a kind of shorthand known as a chemical formula. Ex: Water, H 2 O, contains two atoms of hydrogen for each atom of oxygen. Ex:The formula for table salt, NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio. *When no subscript is present, 1 is understood.

2-1 The Nature of Matter Slide 25 of 40 Copyright Pearson Prentice Hall Chemical Bonds What are the two main types of chemical bonds?

2-1 The Nature of Matter Slide 26 of 40 Copyright Pearson Prentice Hall Chemical Bonds Def: The atoms in compounds are held together by chemical bonds. *Bond formation involves the electrons that surround each atomic nucleus. These are called Valence electrons.

2-1 The Nature of Matter Slide 27 of 40 Copyright Pearson Prentice Hall Chemical Bonds The main types of chemical bonds are: ionic bonds covalent bonds

2-1 The Nature of Matter Slide 28 of 40 Copyright Pearson Prentice Hall Chemical Bonds Ionic Bonds Def: An ionic bond is formed when one or more electrons are transferred from one atom to another. *An atom that loses electrons has a positive charge. *An atom that gains electrons has a negative charge. These positively and negatively charged atoms are known as ions.

2-1 The Nature of Matter Slide 29 of 40 Copyright Pearson Prentice Hall Chemical Bonds Protons +17 Electrons - 18 Charge -1 Protons +11 Electrons - 11 Charge 0 Protons +11 Electrons - 10 Charge +1 Protons +17 Electrons - 17 Charge 0 Chloride ion (Cl - ) Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+)

2-1 The Nature of Matter Slide 30 of 40 Copyright Pearson Prentice Hall Chemical Bonds Covalent Bonds *Sometimes electrons are shared by atoms instead of being transferred. Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms.

2-1 The Nature of Matter Slide 31 of 40 Copyright Pearson Prentice Hall Chemical Bonds A covalent bond forms when electrons are shared between atoms. 1 When the atoms share two electrons, the bond is called a single covalent bond. Ex: C-C 2 When atoms share four electrons it is called a double bond. Ex: C C 3 When atoms share six electrons it is called a triple bond. Ex: C C

2-1 The Nature of Matter Slide 32 of 40 Copyright Pearson Prentice Hall Chemical Bonds Def: The structure that results when atoms are joined together by covalent bonds is called a molecule. *A molecule is the smallest unit of most compounds.

2-1 The Nature of Matter Slide 33 of 40 Copyright Pearson Prentice Hall Chemical Bonds In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom.

2-1 The Nature of Matter Slide 34 of 40 Copyright Pearson Prentice Hall Chemical Bonds Van der Waals Forces *When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. Chemists call such intermolecular forces of attraction van der Waals forces, after the scientist who discovered them.

2-1 The Nature of Matter Slide 35 of 40 Copyright Pearson Prentice Hall Chemical Bonds Although van der Waals forces are not as strong as ionic bonds or covalent bonds, they can hold molecules together, especially when the molecules are large.

2-1 The Nature of Matter Slide 36 of 40 Copyright Pearson Prentice Hall Chemical Bonds *For example, van der Waals forces form between the molecules on the surface of a gecko’s foot and the molecules on the surface of the wall. The combined strength of all the van der Waals forces allows the gecko to grip the wall.

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Slide 38 of 40 Copyright Pearson Prentice Hall 2-1 The particles that move around the nucleus of an atom are called a.neutrons. b.protons. c.electrons. d.isotopes.

Slide 39 of 40 Copyright Pearson Prentice Hall 2-1 The atomic number of a carbon atom is 6. How many neutrons does the isotope carbon-14 have? a.6 b.8 c.12 d.14

Slide 40 of 40 Copyright Pearson Prentice Hall 2-1 Which of the following statements about the three isotopes of carbon is true? a.They are all radioactive. b.They have different numbers of electrons. c.They have the same chemical properties but differ in atomic mass. d.They have the same number of protons and neutrons.

Slide 41 of 40 Copyright Pearson Prentice Hall 2-1 A chemical compound consists of a.electrons mixed with neutrons. b.two or more elements combined in a definite proportion. c.two or more elements combined in any proportion. d.at least three elements combined by ionic or covalent bonds.

Slide 42 of 40 Copyright Pearson Prentice Hall 2-1 Van der Waals forces are the result of a.unequal sharing of electrons. b.ionic bonds. c.the bonding of different isotopes. d.the chemical combination of sodium and chlorine.

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