Forming Chemical Bonds

Transcription

1 Forming Chemical Bonds

2 Why do atoms form chemical bonds? so that the system can achieve the lowest possible potential energy Example covalent bonding in H 2 H H

3 Potential energy 0 Distance of separation between atoms

4 Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound Pearson Education, Inc. Atoms, Molecules, and Ions

5 Ions and Ionic Compounds

6 Ionic compounds Any compound when melted that conducts electricity is considered ionic Example : NaCl (s) NaCl ( l) NaCl ( s) is made up of Na + and Cl - ions

7 Ionic Bonds especially prevalent in compounds formed between group 1A and 2A elements with group 6A and 7A elements. between Elements with the biggest difference in electronegativity

8 Ionic and Molecular Compounds Ionic compounds are usually formed between metals and nonmetals. Molecular compounds are usually formed between two nonmetals.

9 Ions When electrons are removed from or added to a neutral atom or molecule, a charged particle called an ion is formed.

10 Positively charged ions are called cations Negatively charged ions are called anions

11 Atoms vs Ions Na: 11 protons; 11 electrons Cl: 17 protons; 17 electrons + Na + : 11 protons; 10 electrons Cl : 17 protons; 18 electrons

12 Ions positively charged: cations most common type is metal cation Na +, Ca 2+, Al 3+, Fe 2+, Fe 3+ negatively charged: anions most common type is nonmetal anion Cl, O 2

13 Ionic Bonding electrostatic attraction between oppositely charged ions + cation anion

14 Ionic Compounds discrete molecules are not present, so ionic compounds are represented by their empirical formulas some times referred to as formula units

15 Chemical Formulas Express the composition of molecules and ionic compounds in terms of the symbols for the elements they contain. Empirical formula tells us which elements are present and the simplest whole-number ratio of their atoms.

16 Types of Formulas Structural formulas show the order in which atoms are bonded. Perspective drawings also show the three-dimensional array of atoms in a compound Pearson Education, Inc. Atoms, Molecules, and Ions

17 Structure of solid NaCl. In reality, the cations are in contact with the anions. The smaller spheres (red) represent Na + ions and the larger spheres (purple) the Cl ions.

18 Structure of solid NaCl.

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20 Ions When atoms lose or gain electrons, they become ions. Cations are positive and are formed by elements on the left side of the periodic chart. Anions are negative and are formed by elements on the right side of the periodic chart Pearson Education, Inc. Atoms, Molecules, and Ions

21 Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals Pearson Education, Inc. Atoms, Molecules, and Ions

22 Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way: The charge on the cation becomes the subscript on the anion. The charge on the anion becomes the subscript on the cation. If these subscripts are not in the lowest wholenumber ratio, divide them by the greatest common factor Pearson Education, Inc. Atoms, Molecules, and Ions

23 Common Cations 2012 Pearson Education, Inc. Atoms, Molecules, and Ions

24 Common Anions 2012 Pearson Education, Inc. Atoms, Molecules, and Ions

25 Molecules: Atoms in Combination

26 Definition Molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces. bonds structure

27 Chemical Formulas Express the composition of molecules and ionic compounds in terms of the symbols for the elements they contain. Empirical formula tells us which elements are present and the simplest whole-number ratio of their atoms. Molecular formula gives the exact number of atoms each element in the compound

28 Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals Pearson Education, Inc. Atoms, Molecules, and Ions

29 A molecule is not necessarily a compound. Example H 2 O 2 Cl 2 A compound is not necessarily molecular. ionic compounds

30 Diatomic Molecules These seven elements occur naturally as molecules containing two atoms: Hydrogen Nitrogen Oxygen Fluorine Chlorine Bromine Iodine 2012 Pearson Education, Inc. Atoms, Molecules, and Ions

31 Hydrogen stable form of element is diatomic molecule H 2

32 Hydrogen the stable form of the element is diatomic a molecule H 2 The subscript indicates the number of atoms in the formula ball-and-stick model space-filling model other diatomic elements include O 2, N 2, F 2, Cl 2, Br 2, and I 2

33 Water (H 2 O) is a polyatomic molecule (contains three atoms connected in the order HOH).

34 Methane Molecular formula: CH 4 shows the way in which the atoms are joined H H C H H structural formula ball-and-stick model space-filling model

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