Atoms and Bonding The Building Blocks of Matter Matter may consist of elements, compounds, or mixtures. Compound: a substance made of two or more elements chemically bonded together. Mixture: a physical combination of two or more pure substances (i.e., elements or compounds). Element: a substance made of only one type of atom Atoms and Bonding Atomic Theory and Models Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces. Atoms and Bonding Atomic Theory and Models Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere. Atoms and Bonding Atomic Theory and Models Rutherford was surprised that a few particles were deflected strongly. This led him to propose an atomic model with a positively charged nucleus. Atoms and Bonding Atomic Theory and Models Through the first part of the twentieth century, atomic models continued to change. Atoms and Bonding - Atoms, Bonding, and the Periodic Table * Valence Electrons: the electron(s) in the outer shell of an atom’s electron cloud, which can combine with other atoms to form molecules *The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms. Atoms and Bonding Atoms and Bonding The Periodic Table Elements are organized into rows and columns based on their atomic number. Atoms and Bonding - Atoms, Bonding, and the Periodic Table Periodic Table Activity http://www.phschool.com/webcodes10/index.cfm?wcprefix=c gp&wcsuffix=1032&area=view&x=15&y=7 Click to open a browser window and access Active Art about the periodic table. Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table As the number of protons (atomic number) increases, the number of electrons also increases. As a result, the properties of the elements change in a regular way across a period. Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table The variety of colors in a “neon” sign results from passing an electric current through sealed glass tubes containing different noble gases. Atoms and Bonding Ions and Ionic Bonds You and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear. Atoms and Bonding - Ionic Bonds Ions and Ionic Bonds When an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion. Atoms and Bonding Graphic Organizer Polar Covalent Bond Nonpolar Covalent Bond Metallic Bond Equal sharing of electrons Attraction between positive ions and surrounding electrons. Feature Ionic Bond How Bond Forms Attraction between oppositely charged ions Unequal sharing of electrons Charge on Bonded Atoms? Yes; positive or negative Yes, slightly positive or slightly No negative Yes; positive Example NaCl crystal (or other ionic compound) H2O molecule (or other polar covalent molecule) Calcium (or other metal) O2 molecule Atoms and Bonding - Ionic Bonds Ions and Ionic Bonds Ions are atoms that have lost or gained electrons. Atoms and Bonding - Ionic Bonds Ionic bonding is the process of two or more atoms losing or gaining electrons to become charged ions. The charged ions are then attracted to each other: Na + Cl -> Na+Cl- Atoms and Bonding - Ionic Bonds Properties of Ionic Compounds In general, ionic compounds are hard, brittle crystals that have high melting points. When dissolved in water or melted, they conduct electricity. Atoms and Bonding - Covalent Bonds Non-Polar Covalent Bonds: chemical bonding defined as the equal sharing of electrons by two or more atoms to produce a shared attraction. The atoms tend to share electrons, so as to fill the outer electron shell, which can hold up to eight electrons (except for hydrogen and helium, which can accommodate only 2 electrons in the outer shell). Atoms and Bonding - Covalent Bonds How Covalent Bonds Form An oxygen molecule contains one double bond, while a carbon dioxide molecule has two double bonds. A nitrogen molecule contains one triple bond. Atoms and Bonding - Covalent Bonds Unequal Sharing of Electrons Fluorine forms a nonpolar bond with another fluorine atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar. Atoms and Bonding - Covalent Bonds Unequal Sharing of Electrons A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape. Atoms and Bonding - Bonding in Metals Metallic Bonding A metal crystal consists of positively charged metal ions embedded in a “sea” of valence electrons. Atoms and Bonding - Bonding in Metals Metallic Properties The “sea of electrons” model of solid metals explains their ability to conduct heat and electricity, the ease with which they can be made to change shape, and their luster.