1. Chemical Bonds join atoms together 4.3

2. Ionic Bonds One type of chemical bond, an ionic bond, occurs when an atom transfers an electron to another atom.ionic bond Table salt, or sodium chloride (NaCl), is a compound formed as a result of electron transfer between sodium (Na) atoms and chlorine (Cl) atoms. One type of chemical bond, an ionic bond, occurs when an atom transfers an electron to another atom.ionic bond Table salt, or sodium chloride (NaCl), is a compound formed as a result of electron transfer between sodium (Na) atoms and chlorine (Cl) atoms.

3. The transfer of an electron from a sodium atom to a chlorine atom results in oppositely charged ions. The attraction between these ions is an ionic bond.

4. Then the two atoms collide, the chlorine atom strips away sodium's outer electron. In the process, chlorine's highest energy level, now with 8 electrons, becomes filled. In losing an electron, the sodium atom's second energy level, which already has 8 electrons, becomes the highest. It, too, is filled. Then the two atoms collide, the chlorine atom strips away sodium's outer electron. In the process, chlorine's highest energy level, now with 8 electrons, becomes filled. In losing an electron, the sodium atom's second energy level, which already has 8 electrons, becomes the highest. It, too, is filled.

5. Look at how the balance of electric charges has changed. One unit of negative charge (1 electron) moved from sodium to chlorine. The two atoms are now referred to as ions - atoms (or groups of atoms) that have become electrically charged as a result of gaining or losing electrons.ions Look at how the balance of electric charges has changed. One unit of negative charge (1 electron) moved from sodium to chlorine. The two atoms are now referred to as ions - atoms (or groups of atoms) that have become electrically charged as a result of gaining or losing electrons.ions

6. Losing an electron leaves the sodium ion with a charge of 1+, while gaining an electron gives chlorine (now called chloride) a charge of 1-. The attraction holding the oppositely charged Na + and Cl - ions together is the ionic bond. Losing an electron leaves the sodium ion with a charge of 1+, while gaining an electron gives chlorine (now called chloride) a charge of 1-. The attraction holding the oppositely charged Na + and Cl - ions together is the ionic bond.

7. Covalent Bonds In contrast to the transfer of electrons that results in an ionic bond, a covalent bond forms when two atoms share electrons. Electron sharing can be modeled using element symbols, with dots representing the atoms' outermost electrons (Figure 4-9). In contrast to the transfer of electrons that results in an ionic bond, a covalent bond forms when two atoms share electrons. Electron sharing can be modeled using element symbols, with dots representing the atoms' outermost electrons (Figure 4-9).

8. A pair of electrons (dots) between atoms represents a covalent bond. The electron pair counts in the total of outermost electrons for both atoms. You can count 8 electrons around the oxygen atom on the bottom right. Its highest energy level is filled as a result of sharing electrons with the hydrogen atoms.

9. Numbers of Bonds The number of bonds an atom can form usually equals the number of additional electrons that will fill its highest energy level. A hydrogen atom can accept one additional electron, so it can form one bond. In contrast, an oxygen atom can accept two electrons in its highest energy level, so it can form two bonds. The number of bonds an atom can form usually equals the number of additional electrons that will fill its highest energy level. A hydrogen atom can accept one additional electron, so it can form one bond. In contrast, an oxygen atom can accept two electrons in its highest energy level, so it can form two bonds.

10. Molecules Two or more atoms held together by covalent bonds form a molecule. Molecules can be modeled in different ways (Figure 4-10). A chemical formula tells you the number and types of atoms in a molecule.molecule Two or more atoms held together by covalent bonds form a molecule. Molecules can be modeled in different ways (Figure 4-10). A chemical formula tells you the number and types of atoms in a molecule.molecule

11. A structural formula indicates how atoms in a molecule are linked by bonds. Each line between symbols represents a single covalent bond - shared pair of electrons. Double or even triple bonds form when two atoms share two or three pairs of electrons between them. A structural formula indicates how atoms in a molecule are linked by bonds. Each line between symbols represents a single covalent bond - shared pair of electrons. Double or even triple bonds form when two atoms share two or three pairs of electrons between them.

12. A space-filling model, in which color-coded spheres symbolize atoms, is a drawing that depicts a three-dimensional model of a molecule.

13. Some molecules consist of atoms of only one element, as in molecules of hydrogen (H 2 ) and oxygen (O 2 ). However, most molecules are made of two or more different types of atoms, as in water (H 2 O).

14. Chemical Reactions Such changes, which result in the formation of one or more new substances, are called chemical reactions. chemical reactions Some chemical reactions absorb more energy than they release, while others release more energy than they absorb. Such changes, which result in the formation of one or more new substances, are called chemical reactions. chemical reactions Some chemical reactions absorb more energy than they release, while others release more energy than they absorb.

15. Space-filling models for molecules of hydrogen, oxygen, and water illustrate the chemical reaction that is described by the equation. A water molecule always consists of hydrogen atoms and oxygen atoms in a ratio of 2 to 1.

16. Just like a math equation, such as 1 + 1 = 2, you read this equation from left to right. It states that two molecules of hydrogen (2 x H 2 ) react with one molecule of oxygen (O 2 ), forming two molecules of water (2 x H 2 O). Just like a math equation, such as 1 + 1 = 2, you read this equation from left to right. It states that two molecules of hydrogen (2 x H 2 ) react with one molecule of oxygen (O 2 ), forming two molecules of water (2 x H 2 O).

17. The starting materials for the reaction (hydrogen and oxygen) are called reactants.reactants The ending materials (in this case, only water) are called products.products The starting materials for the reaction (hydrogen and oxygen) are called reactants.reactants The ending materials (in this case, only water) are called products.products

18. Notice that the same number of hydrogen atoms (4) is present on both sides of the equation, although the atoms are combined in different molecules. The same is true of the oxygen atoms (2 on each side). Notice that the same number of hydrogen atoms (4) is present on both sides of the equation, although the atoms are combined in different molecules. The same is true of the oxygen atoms (2 on each side).