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chemical bond |
a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. |
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Why are most atoms chemically bonded to one another? |
most atoms have a relatively high potential energy nature prefers lower energy states atoms are therefore less stable when by themselves than when they are bonded with other atoms |
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How do atoms bond? |
valence electrons are redistributed to make the atom more stable |
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ionic bonds |
chemical bonding that results from the electrical attraction between cations and anions atoms completely give up electrons to other atoms |
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covalent bonding |
atoms are sharing their electrons electrons are "owned" equally |
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The degree to which bonding between bonded atoms are covalent or ionic can be determined by |
calculating the difference of the elements’ electronegativities |
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electronegativity difference of 1.7 or less |
covalent |
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Bonding between atoms of the same element |
covalent |
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nonpolar covalent bond |
a covalent bond in which the bonding electrons are shared equally by bonded atoms, resulting in a balanced destribution of electric charge |
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electronegativity differences between 0 and 0.3 |
nonpolar covalent bonds |
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polar |
having uneven distribution of charge |
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polar-covalent bond |
a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons |
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What is the main distinction between ionic and covalent bonding? |
In ionic bonding there is a transfer of electrons and ions are formed, while in covalent bonds there is a sharing of electrons between the two atoms. |
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How is electronegativity used in determining the ionic or covalent character of the bonding between the two elements? |
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Li and F |
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Cu and S |
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I and Br |
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Chemical Bond |
•A link between atoms that results from the attraction of nuclei for electrons -Electrostatic attraction between proton and electron (recall favorable electron affinity of almost all atoms) -Classified/predicted by the way the valence e- are distributed around nuclei of combined atoms |
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Why do atoms bond? |
•Atoms will bond in order to lower their potential energy. Atoms reach lower potential energy by adopting/experiencing the electron configuration of a noble gas atom Atoms strive to reach an octet through chemical bonding |
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Ionic |
-A chemical bond resulting from electrostatic attraction between cations and anions -In a pure ionic bond, one atom completely gives up one or more e- to another atom (rarely happens) -Illustration: A + B A+ + B- |
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Covalent |
-Chemical bond resulting from the sharing of valence electrons between two atoms -In a pure covalent the electrons are shared equally between the two atoms (called nonpolar covalent) -Most covalent result in the electrons being shared unequally between atoms (called polar covalent) |
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Bonding |
•No bond is completely ionic and is rarely completely covalent -Bonds range between the two extremes -Degree of ionic or covalent estimated by comparing electronegativities (EN1 – EN2) |
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Ionic or Covalent? |
•Greater the difference, the more ionic the bond -Range of 1.71—4.0 considered ionic -Examples: Cs + F 4.0 ( F electroneg.) – .7 (Cs electroneg) = 3.3 Ionic bond formed Cs becomes cation, F becomes anion |
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Covalent bonds occur if |
the difference (EN1 – EN2) is less than 50% of larger EN |
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Types of covalent |
-Nonpolar »A covalent bond in which the bonding electrons are shared equally by bonded atoms, with a resulting balanced distribution of electrical charge »Occur with a 0% to 5% ionic character »Range of difference falls between 0-0.3 A bond between 2 identical atoms is completely covalent; electrons are shared equally |
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Polar |
-Polar »Pole = unequal distribution of charge »Polar covalent bond is a bond where united atoms have an unequal attraction for the shared electrons; EN1 – EN2 is ~0.2 – 2 »Range of difference (EN1 – EN2) spans 5%-~50% ionic character A bond between two non-identical atoms can be polar covalent; electrons are shared unequally |
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H to H |
2.1 -2.1= 0 nonpolar covalent bond |
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•H to Cl |
3.3.0 -2.1= 0.9 polar covalent bond Because Cl is more electronegative, it has a stronger attraction for the e-, thus an uneven pull of electrons occurs—however e- still shared (not completely transferred) |
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Uneven sharing |
causes a partial positive and a partial negative pole |
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Metallic Bonding |
-In a liquid or solid state, metals readily give up electrons (low IE) -When only other metal atoms are around, electrons are not accepted and held (low EA), they are free to move -Collection of free moving electrons are called an electron sea—reason for metallic properties of luster, malleability, ductility, and conductivity |
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Linking Bond Character to the Periodic Table of the Elements |
•Polar covalent and nonpolar covalent bonding most readily occurs between nonmetals (e.g., two p-block atoms) •Ionic most readily occurs between metals and nonmetals (e.g., s-block and p-block) •Metallic occurs between metals (i.e. non-metals do not form metallic bonds) |
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molecule |
neutral group of atoms held together by covalem |
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molecular compound |
a chemical compound whose simplest units are molecules |
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chemical formula |
indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts. |
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molecular formula |
shows the types and numbers of atoms combined in a single molecule of a molecular compound. H20 A single water molecule consists of one oxygen atom conjoined by separate covalent bonds from two hydrogen atoms |
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diatomic molecule |
molecule containing only two atoms |
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why does nature favor chemical bonding? |
atoms have lower potential energy when they are chemically bonded |
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Comparing Monatomic, Diatomic, and Polyatomic Molecules |
Monatomic – made of only one atom Diatomic molecules – a molecule containing only two atoms Polyatomic Molecules – a molecule containing more than two atoms |
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Formation of a Covalent Bond |
Section 2: Covalent Bonding & Molecular Compounds Formation of a Covalent Bond Most atoms have lower potential energy when they are bonded to other atoms than they have as they are independent particles. The figure below shows potential energy changes during the formation of a hydrogen-hydrogen bond. |
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Formation of a Covalent Bond |
The electron of one atom and proton of the other atom attract one another. o The two nuclei and two electrons repel each other. o These two forces cancel out to form a covalent bond at a length where the potential energy is at a minimum. |
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Characteristics of the Covalent Bond |
The distance between two bonded atoms at their minimum potential energy (the average distance between two bonded atoms) is the bond length. In forming a covalent bond, the hydrogen atoms release energy. The same amount of energy must be added to separate the bonded atoms Bond energy is the energy required to break a chemical bond and form neutral isolated atoms. |
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Characteristics of the Covalent Bond |
When two atoms form a covalent bond, their shared electrons form overlapping orbitals. This achieves a noble- gas configuration. The bonding of two hydrogen atoms allows each atom to have the stable electron configuration of helium, 1s2. |
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The Octet Rule |
Noble gas atoms are unreactive because their electron configurations are especially stable. This stability results from the fact that the noble-gas atoms’ outer s and p orbitals are completely filled by a total of eight electrons. Other atoms can fill their outermost s and p orbitals by sharing electrons through covalent bonding. Such bond formation follows the octet rule: Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level. |
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Exceptions to the Octet Rule: |
Exceptions to the octet rule include those for atoms that cannot fit eight electrons, and for those that can fit more than eight electrons, into their outermost orbital. Hydrogen forms bonds in which it is surrounded by only two electrons. Boron has just three valence electrons, so it tends to form bonds in which it is surrounded by six electrons. Main-group elements in Periods 3 and up can form bonds with expanded valence, involving more than eight electrons. |
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Electron-Dot Notation |
To keep track of valence electrons, it is helpful to use electron-dot notation. Electron-dot notation is an electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol. The inner-shell electrons are not shown |
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which orbitals usually form bonds? |
single-ocupied orbitals |
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by forming bonds |
there is a decrease in potential energy |
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group 16 |
forms two bonds to gain two electrons and reach noble gas configuration |
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molecular formula |
tells us the size of the molecule |
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chemical formula |
tells us the ratio of the atoms of the elements in the molecule |
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Why is Boron not following the octet rule? |
It is very small and does not lose electrons easily. |
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Aluminum does not follow the octet rule: |
Aluminum loses its electrons more easily than Boron loses three electrons with a reasonable amount of energy plus three cation |
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ionic compound |
is composed of both positive and negative ions that are combined so that the numbers of positive and negative charges are equal most exist as crystalline solids |
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Formula Unit |
the simplest collection of atoms from which an ionic compound’s formula can be established |
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ions minimize pe by |
arranging in a crystal lattice structure |
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ionic compound |
Most of the rocks and minerals that make up Earth’s crust consist of positive and negative ions held together by ionic bonding. • example: table salt, NaCl, consists of sodium and chloride ions combined in a one-to-one ratio— Na+Cl-—so that each positive charge is balanced by a negative charge. Ionic bond is formed when electrons are TRANSFERRED from one atom to the other • An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. |
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Ionic Compounds |
Most ionic compounds exist as crystalline solids. • A crystal of any ionic compound is a three- dimensional network of positive and negative ions mutually attracted to each other. • In contrast to a molecular compound, an ionic compound is not composed of independent, neutral units that can be isolated. |
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Ionic Compounds, continued |
The chemical formula of an ionic compound represents not molecules, but the simplest ratio of the compound’s ions. • A formula unit is the simplest collection of atoms from which an ionic compound’s formula can be established. |
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Formation of Ionic Compounds |
Formation of Ionic Compounds Cl Sodium atom Chlorine atom • The sodium atom has one valence electron and the chlorine atom has seven valence electrons. • Atoms of sodium and other alkali metals easily lose one electron to form cations. • Atoms of chlorine and other halogens easily gain one Na |
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Formation of Ionic Compounds, continued |
In an ionic crystal, ions minimize their potential energy by combining in an orderly arrangement known as a crystal lattice. • Attractive forces exist between oppositely charged ions within the lattice. Lattice configuration minimizes repulsion. • Repulsive forces exist between like-charged ions within the lattice. • The combined attractive and repulsive forces within a crystal lattice determine: • the distances between ions • the pattern of the ions’ arrangement in the crystal |
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A Comparison of Ionic and Molecular Compounds |
The force that holds ions together in an ionic compound is a very strong electrostatic attraction. • In contrast, the forces of attraction between molecules of a covalent compound are much weaker. • This difference in the strength of attraction between the basic units of molecular and ionic compounds gives rise to different properties between the two types of compounds. |
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A Comparison of Ionic and Molecular |
Molecular compounds have relatively weak forces between individual molecules. • They melt at low temperatures. • The strong attraction between ions in an ionic compound gives ionic compounds some characteristic properties, listed below. • very high melting points • hard but brittle • not electrical conductors in the solid state, because the ions cannot move |
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polyatomic ion |
a charged group of covalently bonded atoms |
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Give two examples of an ionic compound |
NaCl NO3- |
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Distinguish between ionic compounds and molecules. |
Ionic compounds are held together by the elctrical attraction between positive and negative ions, while molecules are held together by covalent bonds. |
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lattice energy |
energy released when one mole of an ionic crystalline compound is formed from gaseous ions. |
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nonmetals |
are prone to gaining electrons |
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metals |
are prone to giving away electrons |
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boron |
has only five electrons when it forms only three bonds–achieves noble gas notation with six electrons |
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metallic bonding |
the chemical bonding that results from the attraction between metal atoms and the surrounding sea of atoms. |
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why are metals good electrical conductors? |
highly mobile valence electrons of the atoms that make up a metal. Mobility is not possible in molecular compounds, in which valence electrons are localized in electron-pair bonds between neutral atoms |
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the highest levels of most metal atoms |
are occupied by very few electrons vacant orbitals in the atoms’ outer energy levels overlap. Overlapping of orbitals allows valence electrons to roam freely. |
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mobile atoms |
delocalized move freely about the metal’s network of empty atomic orbitals form the sea of electrons |
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metallic properties |
strong absorbers and reflectors of light have a high luster–though the electrons rise to higher energy levels often, they fall back right away. malleable ductile |
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malleability |
the ability for a substance to be hammered or beaten into thin sheets |
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formula unit |
the simplest collection of atoms from which an ion compound’s formula can be established important when not all the ions have the same magnitude of charge |
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metallic bond strength |
varies with the nuclear charge of the metal atoms and number of electrons in the metal’s electron sea |
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enthalpy of vaporization |
the amount of energy absorbed as heat when a specified amount of a substance vaporizes at constant pressure |
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describe the electron sea model of metallic bonding |
metals have very few electrons in their outer energy levels these orbitals overlapp |
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How do ionic compounds form? |
Formation of Ionic Compounds, continued • In an ionic crystal, ions minimize their potential energy by combining in an orderly arrangement known as a crystal lattice. • Attractive forces exist between oppositely charged ions within the lattice. • Repulsive forces exist between like-charged ions within the lattice. • The combined attractive and repulsive forces within a crystal lattice determine: • the distances between ions • the pattern of the ions’ arrangement in the crystal |
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