How do elements join together to form chemical bonds?

Transcription

1 How do elements join together to form chemical bonds?

2 Do you agree or disagree? 1. Chemical bonds that form between atoms involve electrons. 2. The atoms in a water molecule are more chemically stable than they would be as individual atoms. 3. Losing valence electrons can make some atoms more chemically stable

3 Electrons and Energy Levels Why do atoms gain, lose, or share electrons?

4 The Periodic Table Trends (Patterns) Elements on the periodic table are organized in periods (rows) and groups (columns). The periodic table lists elements in order of atomic number, which increases from left to right as you move across a period.

5 The three main regions of elements on the periodic table classify elements as metals, nonmetals, or metalloids. Except for hydrogen, elements on the left side of the table are metals. Nonmetals are on the right side of the table.

6 Atoms Bond A chemical bond is a force that holds two or more atoms together. A valence electron is an outermost electron of an atom that participates in chemical bonding

7 The periodic table can tell you how many valence electrons an atom has.

8 Atoms Bond (cont.) Atoms with eight valence electrons are chemically stable and do not easily react with other atoms. *happy* Atoms that have between one and seven valence electrons are unstable and easily bond with other atoms to form stable compounds. *unhappy* The elements in group 18 are stable, with the exception of helium, noble gases have eight valence electrons and are chemically stable.

9 Summary: All elements want to achieve a full valence shell with 8 electrons to become stable (except for Hydrogen and Helium which need 2 electrons). To become stable they bond.

10 Atoms with less than eight valence electrons become chemically stable by forming a chemical bond to achieve a full outer shell. Let s look at water

11 Atoms gain, lose, or share valence electrons and become chemically stable.

12 Atoms Bond (cont.) Why do atoms gain, lose, or share electrons?

13 Chemical bonds Chemical bonds join atoms together. A covalent bond is a chemical bond formed when two atoms share one or more pairs of valence electrons Covalent bonds are between a nonmetal and a nonmetal.

14 Example of a covalent bond

15 What element is this?

16 A covalent bond forms when atoms share valence electrons. The smallest particle of a covalent compound is a molecule.

17 Water is covalently bonded molecule Water is unique because the atoms do not share electrons equally this gives water different properties.

18 Understanding Ions All atoms that have a equal number of Protons and electrons have no charge. An ion is an atom that is no longer electrically neutral because it has lost or gained valence electrons.

19 Because electrons have a negative charge, losing or gaining an electron changes the overall charge of an atom. Atoms that lose valence electrons become ions with a positive charge. Atoms that gain an electron become ions with a negative charge.

20 Metal atoms, such as sodium, become more stable when they lose valence electrons and form a chemical bond with a nonmetal. What will Na look like when it loses an electron?

21 Sodium atoms have a tendency to lose a valence electron. Chlorine atoms have a tendency to gain a valence electron.

22 Understanding Ions (cont.) Atoms are electrically neutral because they have the same number of protons and electrons. Once an atom gains or loses electrons, it becomes a charged ion.

23 Ionic Bonds Electron Transferring When forming a compound, the nonmetal atoms gain the electrons lost by the metal atoms. The attraction between positively and negatively charged ions in an ionic compound is an ionic bond.

24 An ionic bond forms between Na and Cl when an Na atom transfers an electron to a Cl atom. What happens to the charges of each atom when they gain or lose electrons?

25 Metallic Bonds Electron Pooling A metallic bond is a bond formed when many metal atoms share their pooled valence electrons. Valence electrons in metals are not bonded to one atom. Instead, a sea of electrons surrounds the positive ions.

26 Valence electrons are free to move among all the aluminum (Al) ions.

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29 Elements can join together by sharing, transferring, or pooling electrons to make chemical compounds.