Atoms and Bonding Table of Contents Atoms, Bonding, and the Periodic Table Ionic Bonds Covalent Bonds Bonding in Metals

Atoms, Bonding, and the Periodic Table Elemental Effects The table lists some elements found in the compounds used in rockets. It shows the effects these elements produce.

What is a Model of the Atom? At the center of the atom is a tiny, dense nucleus containing protons and neutrons. Surrounding the nucleus is a cloudlike region of moving electrons. Most of an atom’s volume is the space in which the electrons move.

Particle Charges Protons are shown by a plus sign- they have a charge of +1 Electrons have exactly the opposite charge of -1. The number of protons equals the number of electrons. The charges between the electrons and protons balance making them neutral. Neutrons don’t affect the charge of an atom because they have a charge of zero.

Comparing Particle Masses A proton and neutron are about equal in mass. Together the protons and neutrons make up almost all the mass of an atom. Electrons would need 1,840 of them to equal 1 proton. Scientists use atomic mass units or (amu) to describe the mass of atom particles.

Atomic Number Every atom of an element has the same number of protons. The number of protons in the nucleus of an atom is the atomic number of that atom’s element.

What Determines an Element’s Chemistry? Valence Electrons The number of protons in a neutral atom equals the number of electrons. Electrons at higher energy levels have higher amounts of energy. The valence electrons of an atom are those electrons that have the highest energy. Valence electrons are involved in chemical bonding. The number of valence electrons in each atom helps determine the chemical properties of that element.

Electron Dot Diagram Each atom of an element has a certain number of valence electrons. Different elements can have 1 to 8 valence electrons. An electron dot diagram includes the symbol for the element surrounded by dots. Each dot stands for one valence electron.

Atoms, Bonding, and the Periodic Table Electron Dot Diagrams The valence electrons of an atom are shown as dots around the symbol of the element. Complete the electron dot diagram for neon.

Bonding Atoms tend to be more stable if they have 8 valence electrons. Atoms tend to form bonds so that they have 8 valence electrons and become more stable. When atoms bond, valence electrons may be transferred from one atom to another. They can also be shared between atoms. Chemical bond is the force of attraction that holds atoms together as a result of the rearrangement of electrons between them.

Apply the Periodic Table Rows are called periods Columns are called groups The elements are in the periodic table in order by increasing atomic number The number of valence electrons increases from left to right across each period. Each period begins with an element that has 1 valence electron. In most cases, the elements within a group always have the same number of valence electrons and therefore have similar properties.

Atoms, Bonding, and the Periodic Table Periodic Table of the Elements The periodic table is arranged in order of increasing atomic number. The number of valence electrons also increases from left to right across a period. What is the number of valence electrons for each group?

Atoms, Bonding, and the Periodic Table The symbols for the elements in Periods 2 and 3 are shown below. Complete the electron dot diagrams for nitrogen, oxygen, fluorine, sodium, magnesium, aluminum, silicon, and argon.

Noble Gases Group 18 are the noble gases. They have 8 valence electrons, except for helium, which has 2. They are stable Unlikely to gain or lose electrons or to share electrons with other atoms. Do not react easily with other elements.

Metals Metal atoms react by losing their valence electrons The reactivity of a metal depends on how easily its atoms lose valence electrons The reactivity of metals decreases from left to right across the periodic table Group 1 is the alkali metals which are the most reactive group. Atoms of alkali metals have only 1 valence electron.

Nonmetals Nonmetal atoms become stable when they gain or share enough electrons to have 8 valence electrons. Nonmetals usually combine with metals by gaining electrons Nonmetals can also combine with other nonmetals and metalloids by sharing electrons Atoms of Group 17 are the halogen and have 7 valence electrons. Halogens react easily with other elements.

Metalloids Metalloids lie between the metals and the nonmetals. Atoms of metalloids can either lose or share electrons when they combine with other elements. Each metalloid has some of the properties of metals and some of the properties of nonmetals.

Atoms, Bonding, and the Periodic Table Groups of Elements

Hydrogen Hydrogen is put in group 1 because it has 1 valence electron but it is a nonmetal. Properties of hydrogen are different from those of alkali metals. Hydrogen shares its electrons when forming compounds with other nonmetals to obtain a stable arrangement of 2 electrons.

How do Ions Form? An ion is an atom or group of atoms that has an electric charge. When a neutral atom loses a valence electron, it loses a negative charge. It becomes a positive ion. When a neutral atom gains an electron, it gains a negative charge. It become a negative ion.

Ionic Bonds How Ions Form An atom that loses one of its electrons becomes a positively charged ion. The atom that gains the electron becomes a negatively charged ion.

Ions Metal atoms are likely to lose electrons Nonmetal atoms are likely to gain electrons

Common Ions Ions that are made of more than 1 atom are called polyatomic ions. Prefix poly means many Polyatomic therefore means many atoms Polyatomic ions have an overall positive or negative charge

Ionic Bonds Ions The table lists the names of some common ions, their charges, and their symbols.

Ionic Bonds When atoms that easily lose electrons react with atoms that easily gain electrons, valence electrons are transferred from one type of atom to another. The transfer gives each type of atom a more stable arrangement of electrons. Ionic bond- the attraction between two oppositely charged ions Ionic compound- the compound that results from an ionic bond In an ionic compound the total positive charge of all the positive ions equals the total negative charge of all the negative ions.

Ionic Bonds Formation of an Ionic Bond Follow the steps to see how an ionic bond forms between a sodium atom and a chlorine atom. Complete the electron dot diagrams.

Ionic Bonds A Maze of Ions What are three pairs of oppositely charged ions? What would the electron dot diagrams be for the ionic compounds?

How are the Formulas and Names of Ionic Compounds Written? A chemical formula is a group of symbols that shows the ratio of elements in a compound. When ionic compounds form, the ions combine to balance the charges on the ions. Subscripts tell the ratio of elements in a compound To write the formula for an ionic compound, write the symbol of the positive ion and then the symbol of the negative ion. Add the subscripts that are needed to balance the charges. If no subscript is written, it is understood that the subscript is 1.

Naming Ionic Compounds For an ionic compound, the name of the positive ion comes first, followed by the name of the negative ion. The name of the positive ion is usually a metal. If the negative ion is a single element, the end of its name changes to –ide. If the negative ion is polyatomic, its name usually ends in –ate or –ite.

Ionic Bonds Use the periodic table to complete the table.

What are Properties of Ionic Compounds Compounds have properties that are different from their component elements. In general, ionic compounds form hard, brittle crystals that have high melting points. They conduct electric current when dissolved in water or melted.

Ionic Crystals Ionic compounds form solids by building up repeating patterns of ions. The ions form an orderly, three-dimensional arrangement called a crystal. Every ion in an ionic compound is attracted to ions of an opposite charge that surround it. Many crystals of ionic compounds are hard and brittle, due to the strength of their ionic bonds and the attractions among all the ions.

Ionic Bonds Halite Ions in ionic compounds are arranged in three-dimensional shapes called crystals. Some have a cubic shape.

Ionic Bonds Galena Galena, or lead sulfide (PbS), has a structure similar to that of table salt.

High Melting Points The ions in the crystal have to break apart for an ionic compound to melt. The energy required to break apart ions is great, causing a high melting point for ionic compounds.

Electrical Conductivity Electric current is the flow of charged particles When ionic crystals dissolve in water, the ions are free to move about, and the solution can conduct current. Ionic compounds in solid form do not conduct current well. If charged particles cannot move, there is no current.

How Are Atoms Held Together in a Covalent Bond? The chemical bond formed when 2 atoms share electrons is called a covalent bond. Covalent bonds usually form between nonmetal atoms. Ionic bonds usually form when a metal combines with a nonmetal.

Electron Sharing The attractions between the shared electrons and the protons in the nucleus of each atom hold the atoms together in a covalent bond. A molecule is a neutral group of atoms joined by covalent bonds. Atoms form molecules that range in size from two to thousands of compounds.

Covalent Bonds Sharing Electrons By sharing 2 electrons in a covalent bond, each fluorine atom gains a stable set of 8 valence electrons. Which are the shared electrons that form a covalent bond between the 2 fluorine atoms?

How Many Bonds? 2 atoms sharing 2 pairs of electrons form a double bond. Atoms that share 3 pairs of electrons form a triple bond.

Covalent Bonds Covalent Bonds Atoms can form single, double, and triple covalent bonds by sharing one or more pairs of electrons.

What are Properties of Molecular Compounds? A molecular compound is a compound that is made up of molecules. Unlike ionic compounds, molecular compounds usually do not conduct electric current when melted or dissolved in water. Also, compared to ionic compounds, molecular compounds generally have lower melting points and boiling points.

Poor Conductivity Molecular compounds do not contain charged particles that are available to move, so there is no current.

Low Melting Points and Boiling Points The forces between molecules are much weaker than the forces between ions. Less heat must be added to a molecular solid to separate the molecules and change it from a solid to a liquid.

Covalent Bonds Melting Points of Molecular and Ionic Compounds What information from the table helps to make a bar graph of the melting points of molecular and ionic compounds?

How Do Bonded Atoms Become Partially Charged? Atoms of some elements pull more strongly on the shared electrons of a covalent bond than do atoms of other elements. As a result, the electrons are shared unequally. Unequal sharing of electrons causes covalently bonded atoms to have slight electric charge.

Nonpolar Bonds and Polar Bonds A covalent bond in which electrons are shared equally is a nonpolar bond. When electrons in a covalent bond are shared unequally, the atom with the stronger pull gains a slightly negative charge. The atom with the weaker pull gains a slightly positive charge. A covalent bond in which electrons are shared unequally is a polar bond.

Covalent Bonds Nonpolar and Polar Bonds Hydrogen forms a nonpolar bond with another hydrogen atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does. The bond formed is polar.

Polar Bonds in Molecules A molecule is polar if it has a positively charged end and a negatively charged end. However, not all molecules containing polar bonds are polar overall. Two atoms pulling with equal strength in opposite directions cancel out the charge, making it nonpolar like in a carbon dioxide molecule.

Covalent Bonds Nonpolar and Polar Molecules Both carbon dioxide and water molecules contain polar bonds. Where would + and - signs be placed to show positive and negative charges?

Attractions Between Molecules Polar molecules are connected to each other by weak attractions between their slight negative and positive charges. These attractions are called van der Waals forces. The properties of polar and nonpolar compounds are different because of differences in attractions between their molecules. Polar molecules have higher melting and boiling points than nonpolar molecules.

Covalent Bonds Bonding Determines the Properties of a Substance Complete the information, using water and sodium chloride as examples.

What is the Structure of a Metal Crystal? Most metals are crystalline solids. A metal crystal is composed of closely packed, positively charged metal ions. The valence electrons drift among the ions. Metallic bond- an attraction between a positive metal ion and a the electrons surrounding it.

Bonding in Metals Metallic Bonding The positively charged metal ions are embedded in a “sea” of valence electrons.

What Are Properties of Metals? Almost all metals are solids at room temperature. Metallic bonding explains many of the common physical properties of metals. Properties of metals include a shiny luster, and high levels of malleability, ductility, electrical conductivity, and thermal conductivity.

Luster Polished metals have a shiny and reflective luster, called metallic luster. The luster of a metal is due to its valence electrons.

Malleability and Ductility Metals are ductile, meaning they can be bent easily and pulled into thin strands or wires. They are also malleable, they can be rolled into thin sheets or beaten into complex shapes.

Thermal Conductivity Thermal energy is the total energy of motion of all the particles in an object. Thermal energy flows from warmer matter to cooler matter, this transfer of thermal energy is known as heat. Metals conduct heat easily because the valence electrons within a metal are free to move.

Electrical Conductivity Metals conduct electric current easily because the valence electrons in a metal can move freely among the atoms.

Alloys Alloy is a mixture made of two or more elements, at least one of which is a metal. Alloys are generally stronger and less reactive than the pure metals from which they are made.