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Chapter 8: Elements and Chemical Bonds

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Presentation on theme: "Chapter 8: Elements and Chemical Bonds"— Presentation transcript:

1 Chapter 8: Elements and Chemical Bonds

2 Lesson 1: Electrons and Energy Levels
The Periodic Table Organizes the chemical elements Each block describes basic properties of one element List elements is order by atomic number Elements in each group have similar chemical properties

3 The Periodic Table (continued)
Metals are on the left side of the periodic table. Nonmetals are on the right side of the table. Metalloids are located in a narrow stair- step region between metal and nonmetals


5 Atoms Bond 1. Most of the matter around you is made up of compounds that include two or more different elements 2. A chemical bond is a force that holds atoms together 3. Atoms contain protons with a positive charge, neutrons with a neutral charge, and electrons with a negative charge.

6 Atoms Bond 3. Atoms contain protons with a positive charge, neutrons with a neutral charge, and electrons wit a negative charge a. Electrons are the atomic particles that participate in chemical bonding. b. The amount of energy an electron can have is an energy level. c. Electrons closest to the nucleus have the least energy; electrons farthest fro the nucleus have the most energy. d. The maximum number of electrons in the first energy level, which is closest to the nucleus, is two. The maximum number of electrons in the second energy level is eight. e. The outermost electrons in an atom are involved in chemical bonding. These electrons are less strongly attached to the nucleus.

7 Atoms Bond 4. A valence electron is an outermost electron.
a. The number of valence electrons in an atom tells you how many bonds an atom can form. b. Each element in the same group in the periodic table has the same number of valence electrons.

8 Atoms Bond 5. The electron dot diagram is a model that represents valence electrons in an atom as dots around the element’s chemical symbol. a. To create an electron dot diagram, draw one dot for each electron in the atom, placing one dot on each of the four sides of the symbol and then pairing additional dots. b. The number of unpaired dots in an electron dot diagram tells you how many bonds an atom can form.

9 Atoms Bond 6. Many atoms are stable with eight electrons. An atom with at least one unpaired electron is unstable. a. Stable atoms do not easily react with or form bonds with other atoms. b. Group 18 includes the noble gases; with the exception of helium, each of these gases have eight valence electrons and are stable. c. unstable atoms can become stable only by forming chemical bonds with other atoms. d. atoms tend to gain, lose, or share valence electrons until each atom has the same number of valence electrons as the noble gases. e. stable atoms have four pairs of valence electrons

10 Lesson 2: Compounds, Chemical Formulas, and Covalent Bonds
From Elements to Compounds 1. Compounds are chemical combinations of two or more elements. 2. Compounds and the elements that form them often have different chemical and physical properties. 3. Atoms can bond to form compounds by sharing valence electrons.

11 From Elements to Compounds
4. A chemical formula is a group of chemical symbols and numbers that represent the elements and the numbers of atoms of each element in a compound. 5. The letters in a chemical formula represent elements. 6. Molecular models show the shape and appearance of the arrangement of atoms in a compound

12 Covalent Bonds – Electron Sharing
1. A covalent bond is a chemical bond formed when two or more atoms share one or more pairs of valence electrons. 2. When forming water, valence electrons are shared between oxygen and hydrogen atoms, thereby forming a covalent bond to make three stable atoms.

13 Covalent Compounds 1. a molecule is group of atoms held together by covalent bonding that acts as an independent unit. 2. Covalent compounds generally have low melting points and low boiling points. They are poor conductors of electricity. a. In a hydrogen molecule, a single covalent bond forms when each atoms shares its valence electrons with the other.

14 Covalent Compounds b. In a carbon dioxide molecule, a double covalent bond forms when the carbon atom shares two pairs of valence electrons with each oxygen atom. c. In a triple covalent bond, three pairs of valence electrons are shared between two atoms. d. Triple covalent bonds are stronger than double covalent bonds, which are stronger than single covalent bonds

15 Covalent Compounds 3. In a covalent bond, one atom can attract the shared electrons more strongly than the other atom can. a. In a molecule of water, the oxygen atom attracts the electrons more strongly than each hydrogen atom does. b. Because the electrons have slight negative charge, there is a slight negative charge near the oxygen atom; there is a slight positive charge near the hydrogen atoms.

16 Covalent Compounds 3c. A molecule that has a slight positive end and a slight negative end because of unequal sharing of electrons is a polar molecule. 3d. Polar molecules, such as sugar and water, dissolve easily in one another because of the attraction of opposite charges. 4. Molecules made up of atoms of the same element are nonpolar because the atoms are identical. So they share electrons equally.

17 Ionic Bonds 1. When a metal and a nonmetal bond, they do not share electrons. 2. The metal atom transfers on or more valence electrons to the nonmetal atom, forming a chemically stable compound. 3. an ion is an atom that is no longer electrically neutral because it has lost or gained one or more valence electrons.

18 Ionic Bonds 3a. An atom that loses one or more valence electron becomes an ion with a positive charge. 3b. An atom that gains one or more valence electrons becomes an ion with a negative charge. 4. Sodium is a metal that has one valence electron. 4a. To become stable, sodium has to lose a valence electron. So, when a sodium atom loses a valence electron it becomes a positively charged ion.

19 Ionic Bonds – Electron Transferring
1. When forming a chemical bond, the nonmetal atoms gain the electrons lost by the metal atoms. 2. Due to the change in the number of electrons, the metal and nonmetal atoms both become ions. 3. The attraction between positively and negatively charged ions in anionic compound is an ionic bond.

20 Ionic Compounds 1. Most ionic compounds are solid and brittle at room temperature. a. Ionic compounds usually have high melting points and boiling points. b. Ionic compounds are good conductors of electricity because electric charge passes easily from one ion to another.

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