Forming Chemical Bonds
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
Potential energy 0 Distance of separation between atoms
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. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
Ions and Ionic Compounds
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
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
Ionic and Molecular Compounds Ionic compounds are usually formed between metals and nonmetals. Molecular compounds are usually formed between two nonmetals.
Ions When electrons are removed from or added to a neutral atom or molecule, a charged particle called an ion is formed.
Positively charged ions are called cations Negatively charged ions are called anions
Atoms vs Ions Na: 11 protons; 11 electrons Cl: 17 protons; 17 electrons + Na + : 11 protons; 10 electrons Cl : 17 protons; 18 electrons
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
Ionic Bonding electrostatic attraction between oppositely charged ions + cation anion
Ionic Compounds discrete molecules are not present, so ionic compounds are represented by their empirical formulas some times referred to as formula units
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.
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. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
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.
Structure of solid NaCl.
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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. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
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. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
Common Cations 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
Common Anions 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
Molecules: Atoms in Combination
Definition Molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces. bonds structure
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
Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals. 2012 Pearson Education, Inc. Atoms, Molecules, and Ions
A molecule is not necessarily a compound. Example H 2 O 2 Cl 2 A compound is not necessarily molecular. ionic compounds
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
Hydrogen stable form of element is diatomic molecule H 2
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
Water (H 2 O) is a polyatomic molecule (contains three atoms connected in the order HOH).
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