Chapter 2 Notes The Chemistry of Life

Transcription

1 Name: Chapter 2 Notes The Chemistry of Life Section 2-1 The Nature of Matter Date: Atoms (p. 35) The study of chemistry begins with the basic unit of matter, the. Comes from the Greek word atomos, meaning unable to be cut. Atoms are incredibly. Placed side by side, 100 million atoms would make a row only about 1 long. Atoms contain particles that are even smaller. The subatomic particles that make up atoms are: Have about the same mass 1/1840 mass of a proton Subatomic Particle Charge Location Proton Neutron Electron Electrons are attracted to the charged nucleus, but remain outside the nucleus because of the of their motion. Because atoms have equal numbers of and, and because these subatomic particles have equal but opposite changes, atoms are. 1

2 Elements and Isotopes (p. 36) A chemical is a pure substance that consists entirely of one type of. Elements are represented by a one- or two-letter symbol. stands for carbon. stands for sodium. The number of in an atom of an element is the element s. Carbon has protons, so its atomic number is. More than 100 elements are known, but only about two dozen are commonly found in organisms, such as: Carbon (C) Hydrogen (H) Nitrogen (N) Oxygen (O) Phosphorus (P) Sulphur (S) Calcium (Ca) Chlorine (Cl) Fluorine (F) Iron (Fe) Magnesium (Mg) Silica (Si) Atoms of the same element that differ in the number of they contain are known as. Mass number = the sum of the and in the nucleus of an atom. Isotopes are identified by their numbers. e.g., carbon has three isotopes: carbon-12 carbon-13 carbon-14 How are all of the isotopes of an element similar? All isotopes have a different number of neutrons. Because they have the same number of, all isotopes of an element have the same properties. 2

3 Radioactive Isotopes Some isotopes are, meaning that their nuclei are and break down at constant rate over time. Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses, such as: to determine the of rocks and fossils. to treat. to kill that cause food to spoil. as labels or to follow the movement of substances within an organism. Chemical Compounds (p. 37) In nature, most elements are found combined with other elements in. Compound = a substance formed by the chemical of two or more in definite proportions. The physical and chemical properties of a compound are from the elements from which it is formed. Scientists show the composition of compound using a chemical. Water,, contains two atoms of hydrogen (H) and one atom of oxygen (O). Table salt,, indicates that sodium (Na) and chlorine (Cl) combine in a 1:1 ratio. Chemical Bonds (p. 38) The atoms in compounds are held together by bonds. Bond formation involves the that surround each atomic nucleus. The electrons that are available to form bonds are called electrons. 3

4 The two main types of chemical bonds are: bonds bonds Ionic Bonds An ionic bond is formed when one or more electrons are from one atom to another. An atom that loses electrons has a charge. An atom that gains electrons has a charge. o These positively and negatively charged atoms are called. Covalent Bonds Sometimes electrons are by atoms instead of being transferred. Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms. The compound sodium chloride (NaCl) forms when sodium loses its valence electron to chlorine. The elements become ions when a charge remains. A covalent bond forms when electrons are between atoms. Number of shared electrons Name of covalent bond Single Double Triple 4

5 Molecule = the structure that results when atoms are joined together by bonds. A molecule is the units of most compounds. In a molecule, each hydrogen atom forms a covalent bond with the oxygen atom. Van der Waals Forces When molecules are close together, a can develop between the oppositely charged regions of nearby molecules. Chemists call such intermolecular forces of attraction van der Waals forces. Although van der Waals forces are not as as ionic or covalent bonds, they can hold together, especially when the molecules are large. o For example, van der Waals forces form between the molecules on the surface of a foot and the molecules on the surface of the. The combined of all the van der Waals forces allows the gecko to grip the wall. 5