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Transcript of Chemical Bonding
IV.1 Compounds can be differentiated by their chemical and physical properties.
Chemical and physical properties are used to differentiate compounds. Some of these properties are hardness, conductivity, and melting point.
Chemical properties change the chemical composition of the original matter.
Physical properties include but are not limited to: hardness, texture, and color.
IV.4 In a multiple covalent bond, more than one pair of electrons are shared between two atoms.
Sometimes in order for a atoms to achieve a stable octet or a full outer shell it must share more than one pair of electrons, forming double or triple covalent bonds.
IV.2 Two major categories of compounds are ionic and molecular (covalent) compounds.
An ionic compound is a chemical compound held together by ionic bonds. An ionic bond is a chemical bond formed through an electrostatic attraction between two opposite charged ions.
by Zipporah Osei
VI.3 Chemical bonds are formed when valence electrons are:
transferred from one atom to another (ionic)
IV.6 When an atom gains one ore more electrons, it becomes a negative ion and its radius increases. When an tom loses one or more electrons, it becomes a positive ion and its radius decreases.
IV.11 Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. Electronegativity values are assigned according to arbitrary scales.
Electronegativity is how strongly an element attracts electrons.
IV.12 The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond.
A polar molecule is a molecule that contains an unequal sharing of electrons. This happens when one atom has greater electronegativity value than the other atom. When this happens the shape of the molecule is asymmetrical.
IV.13 Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetals to form molecular (covalent) compounds. Ionic compounds containing polyatomic ions have both ionic and covalent bonding
Ionic bonding between metals and nonmetals happens because most metals have a small number of electrons on their outershell that they are willing to give up, while nonmetals are only in need of a small number of electrons to reach configuration.
Two nonmetals do not have an electronegativity value strong enough to transfer electrons so they simply share them, creating covalent bonds.
IV.7 When a bond is broken, energy is absorbed. When a bond is formed, energy is released.
In order to create a compound, bonds must be formed between atoms. During this bonding process, energy is released in a reaction known as an exothermic reaction. This release occurs because bond formation stabilizes atoms, causing them to lose some of their energy.
If these bonds break, energy is absorbed in the opposite reaction known as an endothermic reaction. In bond breaking, atoms are made less stable so they require more energy.
IV.10 Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions.
Lewis structures show the electrons in an atom, ion, or molecule. In an element or ion, the number of valence electrons is shown. In a molecule, the number of valence electrons as well as the bonds are shown.
IV.9 Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point.
Conductivity- a measure of the ability of an electric current to flow through a substance.
IV.8 Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond.
A stable valence electron configuration is when the outer shell of an atom has eight electrons. In order, to gain all eight electrons, atoms form ionic bonds with other atoms.
For example, the element Na has a configuration of 2,8,1. To have a stable valence electron configuration, Na gives up its one outer electron to become the ion Na+ and have a configuration of 2,8. If Na were to bond with Cl (which has a configuration of 2,8,7) Cl will take the electron that Na has given up. This will make Cl the ion Cl- with a configuration of 2,8,8.
Elements can also bond covalently. Covalent bonds are formed when two elements share share electrons. One example of a covalent bond is O2. Each oxygen atom has 6 electrons. When it joins with another oxygen, it will share in order to reach 8.
A molecular (covalent) compound is a compound in which the atoms that are bonded share electrons to obtain a stable arrangement of electrons.
shared between atoms (covalent)
mobile within a metal (metallic)
Example of a double covalent bond:
Example of a triple covalent bond:
5a. Molecular polarity can be determined by the shape of the molecules and distribution of charge. Symmetrical (nonpolar) molecules include CO2, CH4, and diatomic elements.
Polarity results from the uneven partial charge distribution between various atoms in a compound.
Some compounds can contain polar bonds but can be shaped in a way that make them nonpolar. These are some examples:
Diatomic elements contain nonpolar bonds therefore they are nonpolar.
5b. Asymmetrical (polar) molecules include HCl, NH3, and H20
When electrons are shared unequally, polar bonds are formed. This occurs because the elements in the compound have different electronegativity values. Electronegativity is the measure of an atoms tendency to attract bonded electrons.
The atom with the greater electronegativity will have a negative charge and the atom with a lower electronegativity will have a positive charge.
Noble gases tend not to bond because they already have the eight valence electrons needed to make them stable.
*Metallically bonded molecules have good electric conductivity.
*Molecular substances are poor substances.
*Ionic substances are good conductors when dissolved into aqueous solutions. Solid ions are poor conductors,
Hardness- how hard something is.
*Generally, metallic and ionic solids are hard while molecular solids are soft.
Solubility- the amount of a substance that can be dissolved in a given amount of solvent at a set temperature.
Malleability- capable of being shaped or formed, as by hammering or pressure: a malleable metal
*This property usually applies to the family groups 1 to 12 on the Modern Periodic Table of Elements.
Melting point- the temperature at which both the solid and liquid phases exists at equilibrium
Boiling point- the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure.
As you move left to right on The Periodic Table, electronegativity increases.
As you move down The Periodic Table, electronegativity decreases.
Nonmetals tend to have higher electronegativity values than metals.
Noble gases do not have an electronegativity value because they do not tend to bond.
Example of a polar molecule:
*In CO2, the oxygen atoms have a greater electronegativity value than carbon so the electrons they share are more attracted to oxygen than carbon.
Example of a nonpolar molecule:
*In O2 the electrons are distributed evenly, making it a nonpolar molecule.