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Transcript
9/22/14 Chapter 2: The Chemistry of Life Chapter 2: The Chemistry of Life 2–1 The Nature of Matter Mr. M. Varco St. Joseph High School 2.1: Atoms • What are human made of? – All materials are made of matter (solid, liquid, gas) • The study of chemistry begins with the basic unit of matter, the atom, which is the smallest particle. • Atoms are composed of three sub-atomic particles – Protons (+) – Neutrons ( ) – Electrons (-) 1 9/22/14 2.1: Atoms • Strong forces bind protons and neutrons to form the Nucleus at the center of the atom • Electrons are in constant motion around nucleus, and are attracted to the positively charged nucleus • Despite their charges, atoms themselves are electrically neutral because atoms have equal number of protons and electrons 2.1: Elements and Isotypes • An element is a pure substance that consists entirely of one type of atom. – More than 100 elements are known – Carbon (C), Hydrogen (H), etc. 6 C Atomic Number Carbon 12.011 • Atomic Number: the number of protons in the nucleus of an element • Example: Carbon (C) à Atomic number = à Protons = ? à Electrons = ? 6 2 9/22/14 2.1: Elements and Isotypes Atomic Number 6 C Carbon 12.011 2.1: Elements and Isotypes Recall: Atomic # = Proton # Proton # = Electron # 3 9/22/14 2.1: Elements and Isotypes • All atoms of an element have the same number of protons. However, the number of neutrons of an element’s atoms can vary. • Ex: All atoms of carbon have 6 protons and 6 electrons – Some carbon atoms have 6 neutrons, while other have more. 6 C Carbon 12.011 2.1: Elements and Isotypes • Isotope: Atoms of the same element that differ in the number of neutrons they contain – Isotopes are identified by their mass number • Mass Number: Total number of protons and neutrons in the nucleus of an atom 6 C Carbon 12.011 4 9/22/14 2.1: Elements and Isotypes • Isotope: Atoms of the same element that differ in the number of neutrons they contain – Isotopes are identified by their mass number • Mass Number: Total number of protons and neutrons in the nucleus of an atom Isotope # of Protons # of Neutrons # of Electrons Carbon-12 (nonradioactive) 6 6 6 Carbon-13 (nonradioactive) 6 7 6 Carbon-14 (radioactive) 6 8 6 2.1: Chemical Compounds • Compound: a substance formed by the chemical combination of two or more elements. – Compounds are written in chemical formula: Na + Cl = NaCl • The physical and chemical properties of a compound are usually different from those of the elements from which it was formed H2 Gas + O Gas = H 2O Water 5 9/22/14 2.1: Chemical Bonds • Atoms in a chemical compound are held together by Chemical Bonds • Two main types of chemical bonds in chemistry are: – Ionic Bonds – Covalent Bonds 2.1: Chemical Bonds • Ionic Bonds are formed when one or more electrons are transferred from one atom to another • A loss or gain of electrons results in a positively or negatively charged atom known as an Ion 6 9/22/14 2.1: Chemical Bonds Ionic Bonding Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-) Protons +11 Electrons -10 Charge +1 Protons +17 Electrons -18 Charge -1 Transfer of electron Protons +11 Electrons -11 Charge 0 Protons +17 Electrons -17 Charge 0 2.1: Chemical Bonds • Electrons may be transferred to another atom (Ionic Bonding) or shared between atoms • Covalent Bond: Sharing of electrons between the nuclei of two atoms – Single Covalent Bond (sharing of two electrons) • Molecule: the smallest unit of most compounds, which result when atoms are joined together by covalent bonds. 7