Atoms and Bonding Table of Contents Valence Electrons

Atoms and Bonding Table of Contents Valence Electrons and Bonding The Periodic Table Ionic and Covalent Bonds Molecular Compounds Acids and Bases

Atoms and Bonding Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW Matter – anything that has a mass and takes up space Elements – simplest pure substance that cannot be broken down (one type of atom) Compound – pure substance of two or more elements chemically combined in a specific ratio Mixture – two or more substances in the same area not chemically combined. Atom – smallest particle of an element or the basic unit of matter Protons (+) and Neutrons (o) in the nucleus Electrons (-) orbit outside the nucleus

Atoms and Bonding - Elements and Atoms The Building Blocks of Matter may consist of elements, compounds, or mixtures.

Atoms and Bonding Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW Scientific theory - a well-tested idea that explains and connects a wide range of observations. Model – physical, mental, visual, and other representations of an idea to help people understand a concept that they cannot observe directly.

Atoms and Bonding Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW John Dalton’s Model • All elements are made of atoms that cannot be divided. • All atoms of the same element are exactly alike and have the same mass. Atoms of different elements are different and have different masses. • An atom of one element cannot be changed into an atom of a different element. Atoms cannot be created or destroyed in any chemical change, only rearranged. • Every compound is made of atoms of different elements, combined in a specific ratio.

Atoms and Bonding - Elements and Atoms Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW • Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.

Atoms and Bonding - Elements and Atoms Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW JJ Thomson Model (1897) • Suggested that atoms had negatively charged electrons embedded in a positive sphere.

Atoms and Bonding - Elements and Atoms Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW Earnest Rutherford Model (1911) • Performed an experiment where he shot positively charged particles through a thin sheet of gold foil • Some particles were deflected (same charges repel) • Led him to propose an atomic model with a positively charged nucleus.

Atoms and Bonding Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW Niels Bohr Model (1913) • Showed electrons having specific amounts of energy causing them to stay in certain orbits • Model showed flat orbital planes Orbital Cloud Model– (1920) electrons orbit the nucleus in multiple planes, creating a “negatively charged cloud” • Amount of energy is related to how tightly they are held (increased energy = looser hold)

Atoms and Bonding - Elements and Atoms Ch. 1 Sec. 1 “Elements and Atoms” Book L pgs 6 -11 - REVIEW Modern Atomic Theory (1932) – discovery of neutrons in the nucleus (similar mass to protons but no charge)

Atoms and Bonding - Elements and Atoms More on Atomic Structure Click the PHSchool. com button for an activity about atomic structure.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table Valence Electrons and Bonding • Valence electrons - The electrons that are in the highest energy level of an atom and that are involved in chemical reactions. • 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, Bonding, and the Periodic Table Valence Electrons and Bonding • Electron dot diagram A representation of the valence electrons in an atom, using dots. • Most elements that have a full set of valence electrons are “stable” or “unreactive” • Ex. Noble gases – Neon, Argon, Krypton

Atoms and Bonding - Atoms, Bonding, and the Periodic Table Valence Electrons and Bonding • When the valence shell of an atom is not full, one of two things can happen: 1. It will either take or share electrons from another atom to make it full 2. It will give up some loosely held electrons to make the new valence shell full • Both scenarios make the atom “reactive” and a chemical bond will form • Chemical bond - the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table • The periodic table is a system used worldwide for organizing elements into categories • Elements are organized into rows and columns based on their atomic number.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table • Symbol - one- or two-letter set of characters that is used to identify an element. • Atomic number - the number of protons in the nucleus of an atom. • Elements are arranged in order of increasing atomic number. • Period - elements in the same horizontal row of the periodic table. • Group/family - elements in the same vertical column of the periodic table.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table Activity Click the Active Art button 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. • A period ends when the highest energy level has eight electrons. • The valence electrons of atoms in the next period are in a higher level so atoms in a group always have the same number of valence electrons

Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table • Noble gas - an element of Group 18 of the periodic table. • Typically “unreactive” • 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 - Atoms, Bonding, and the Periodic Table The Periodic Table Reactive Metals/Non-metals • Halogen - an element belonging to Group 17 of the periodic table that has 7 valence electrons • React easily with other elements whose atoms can give up or share electrons. • Alkali metal – an element belonging to group 1 that have only one valence electron • Can become chemically more stable by losing their one valence electron.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table Other Metals • Most have one, two, or three valence electrons. • React by losing these electrons, especially when they combine with oxygen or one of the halogens. Other Non-metals • All of the nonmetals have four or more valence electrons. • Become stable when they gain or share enough electrons to have a set of eight valence electrons.

Atoms and Bonding - Atoms, Bonding, and the Periodic Table The Periodic Table Metalloids • Elements that lie along a zigzag line between the metals and nonmetals • Depending on the conditions, these elements can behave as either metals or nonmetals • Have from three to six valence electrons and can either lose or share electrons when they combine with other elements

Atoms and Bonding - Ionic Bonds Ions and Ionic Bonds • Ion - an atom or group of atoms that has an electric charge • 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 - Ionic Bonds 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 • Polyatomic ion - an ion that is made of more than one atom. • group of atoms that reacts as a unit • have an overall positive or negative charge

Atoms and Bonding - Ionic Bonds Ions and Ionic Bonds • Ionic bond - the attraction between two oppositely charged ions • Form as a result of the attraction between positive and negative ions. • Ionic compound - a compound that consists of positive and negative ions.

Atoms and Bonding - Ionic Bonds Chemical Formulas and Names • Chemical formula - a combination of symbols that represents the elements in a compound. • Subscript - number in a chemical formula that tells the number of atoms in a molecule or the ratio of elements in a compound. • When ionic compounds form, the ions come together in a way that balances out the charges on the ions. The chemical formula for the compound reflects this balance. • For an ionic compound, the name of the positive ion comes first, followed by the name of the negative ion. • Ex: Mg. O is named magnesium oxide; NH 4 NO 3, named ammonium nitrate

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. • Crystal - an orderly, 3 -D pattern of ions or atoms in a solid. • Every ion is attracted to ions of opposite charge that surround it • The pattern remains the same no matter what the size of the crystal • Ions in water can increase the melting point and the electrical conductivity

Atoms and Bonding - Ionic Bonds Salt Click the Video button to watch a movie about salt.

Atoms and Bonding - Ionic Bonds Links on Ionic Compounds Click the Sci. Links button for links on ionic compounds.

Atoms and Bonding - Covalent Bonds How Covalent Bonds Form • Covalent bond – a chemical bond formed when two atoms share electrons. • usually form between atoms of nonmetals • The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons. • Molecule – a neutral particle made of two or more atoms joined by covalent bonds.

Atoms and Bonding - Covalent Bonds How Covalent Bonds Form • The number of covalent bonds that nonmetal atoms can form equals the number of electrons needed to make a total of eight (or a full outer shell) • The oxygen atom in water and the nitrogen atom in ammonia are each surrounded by eight electrons as a result of sharing electrons with hydrogen atoms.

Atoms and Bonding - Covalent Bonds How Covalent Bonds Form • Double bond - a chemical bond formed when atoms share two pairs of electrons. • Triple bond - a chemical bond formed when atoms share three pairs of electrons. • 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 Molecular Compounds • Molecular compound - a compound that is composed of molecules • Compared to ionic compounds, molecular compounds generally have lower melting points and boiling points, and they do not conduct electricity when dissolved in water.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds The table compares the melting points and boiling points of a few molecular compounds and ionic compounds. Use the table to answer the following questions.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds Graphing: Create a bar graph of just the melting points of these compounds. Arrange the bars in order of increasing melting point. The y-axis should start at – 200ºC and go to 900ºC. Check that the graphs are correctly set up and labeled before students plot the data.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds Interpreting Data: Describe what your graph reveals about the melting points of molecular compounds compared to those of ionic compounds. Melting points of molecular compounds are lower than those of ionic compounds.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds Inferring: How can you account for the differences in melting points between molecular compounds and ionic compounds? Molecular compounds have weak attractive force between molecules, so less energy is needed to melt molecular compounds.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds Interpreting Data: How do the boiling points of the molecular and ionic compounds compare? Boiling points of molecular compounds are lower than those of ionic compounds.

Atoms and Bonding - Covalent Bonds Comparing Molecular and Ionic Compounds Predicting: Ammonia’s melting point is – 78ºC and its boiling point is – 34ºC. Is ammonia a molecular compound or an ionic compound? Explain. Students may predict that ammonia is a molecular compound because it has relatively low melting and boiling points.

Atoms and Bonding - Covalent Bonds Unequal Sharing of Electrons • Atoms of some elements pull more strongly on shared electrons than do atoms of other elements. • As a result, the electrons are pulled more toward one atom, causing the bonded atoms to have slight electrical charges. • Polar bond - a covalent bond in which electrons are shared unequally • Nonpolar bond - a covalent bond in which electrons are shared equally.

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 - Covalent Bonds Links on Molecular Compounds Click the Sci. Links button for links on molecular compounds.

Acids, Bases, and Solutions Properties of Acids • Acid – a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus red. • Ex: hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, and acetic acid.

Acids, Bases, and Solutions - Describing Acids and Bases Properties of Acids and Bases Litmus is an example of an indicator, a compound that changes color when in contact with an acid or a base.

Acids, Bases, and Solutions - Describing Acids and Bases Uses of Acids and Bases Acids and bases have many uses around the home and in industry.

Acids, Bases, and Solutions - Describing Acids and Bases Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask a what question for each heading. As you read, write answers to your questions. Question Answer What is an acid? An acid is a substance that tastes sour, reacts with metals and carbonates, and turns blue litmus paper red. What is a base? A base is a substance that tastes bitter, feels slippery, and turns red litmus paper blue. What are uses of acids and bases? Uses of acids include cleaning products, fertilizers, and car batteries; uses of bases include cleaning products, baking ingredients, and cement manufacturing.