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 Placed side by side, 100 million atoms would make a row only about 1 centimeter long. 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 neutrons electrons

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 have about the same mass. Protons are positively charged particles (+). Neutrons carry no charge. Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom.

2-1 The Nature of Matter Slide 9 of 40 Copyright Pearson Prentice Hall Atoms The electron is a negatively charged particle (−) with 1/1840 the mass of a proton. Electrons are in constant motion in the space surrounding the nucleus.

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

2-1 The Nature of Matter Slide 12 of 40 Copyright Pearson Prentice Hall Elements and Isotopes Elements: 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. C stands for carbon. 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. Carbon has 6 protons, so its atomic number is 6. 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 Copyright Pearson Prentice Hall Chemical Compounds In nature, most elements are found combined with other elements in compounds. 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 15 of 40 Copyright Pearson Prentice Hall Chemical Compounds Scientists show the composition of compounds by a kind of shorthand known as a chemical formula. Water, H 2 O, contains two atoms of hydrogen for each atom of oxygen. The formula for table salt, NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio.

2-1 The Nature of Matter Slide 16 of 40 Copyright Pearson Prentice Hall Chemical Bonds What are the two main types of chemical bonds?

2-1 The Nature of Matter Slide 17 of 40 Copyright Pearson Prentice Hall Chemical Bonds The atoms in compounds are held together by chemical bonds. Bond formation involves the electrons that surround each atomic nucleus. The electrons that are available to form bonds are called valence electrons.

2-1 The Nature of Matter Slide 18 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 19 of 40 Copyright Pearson Prentice Hall Chemical Bonds Ionic Bonds 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 20 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 21 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 22 of 40 Copyright Pearson Prentice Hall Chemical Bonds In a water molecule, each hydrogen atom forms a single covalent bond with the oxygen atom.

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Slide 24 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 25 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 26 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 27 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.

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