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Chapter 2: Chemistry of Life 2.1 Composition of Matter • Matter – anything that occupies space and has mass • Mass – the quantity of matter an object has **Mass vs. Weight** 2.1 Composition of Matter Atoms •Atom – the fundamental unit of matter •Components – – Nucleus – central core, most of the mass, consists of proton and neutron – Proton – positive electrical charge – Neutron – no electrical charge – Electrons – negative electrical charge (move around outside of the nucleus) – Overall charge of atom = 0 (protons and electrons cancel each other out) 2.1 Composition of Matter 2.1 Composition of Matter Elements •Elements – substances that cannot be broken down chemically – Atomic number = # of protons in an atom – Example – carbon – each atom of carbon has 6 protons so the atomic # is 6 •Isotopes – atoms of the same element that differ in the number of neutrons – Mass number – sum of protons and neutrons in an atom – Example - 2.1 Composition of Matter • Radioisotopes – isotopes in which the nucleus is unstable and tends to release particles or radiant energy or both – Can help determine age of fossils – Can help trace movement of chemicals through organisms 2.1 Composition of Matter Compounds •Compounds – consist of atoms of 2 or more elements that are joined by a chemical bond – Compounds often times have different properties than the elements within the compound had when by themselves: Sodium Chlorine Sodium Chloride 2.1 Composition of Matter Two Bond Types •Ionic Bonds – electrons move from one atom to another to form a bond – Example – table salt – NaCl – sodium loses and electron and chlorine gains an electron – – + Transfer of electron Na Cl Na Sodium atom Cl Chlorine atom Na Na+ Sodium ion – Cl Cl– Chloride ion Sodium chloride (NaCl) 2.1 Composition of Matter • Covalent Bonds – electrons are shard one or more pairs of electrons – Example – methane – CH4 – electrons are shared in the outer electron shell: