Ions form when electrons are transferred among atoms. For example, a group 1A element, such as potassium, tends to transfer one electron to other atoms, causing it to form a net positive charge, in this case K . Such ions with net positive charges are called cations. Ions with net negative charges are anions. Nonmetal atoms, such as chlorine, tend to accept electrons from other atoms. Chlorine tends to gain a single electron, forming the anion Cl .

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Positive ions are smaller than the atoms from which they are formed, but negative ions are larger than the atoms from which they are formed. Explain why this is so.
When an electron is added to an atom, the attraction of the nucleus for any one electron decreases and the size of the ion"s radius increases. When an electron is removed from an atom, there is an increase in the nuclear attraction experienced by the remaining electrons. Consequently, the remaining electrons are drawn closer to the nucleus.
Describe the trends in electronegativity within groups and across periods in the periodic table. Provide examples
Electronegativity values decrease from top to bottom within a group, and from right to left across a period. For example, rubidium is less electronegative than lithium. Lithium is less electronegative than fluorine.
The electron configurations of the noble gases are extremely stable. The octet rule states that, in chemical reactions, elements gain or lose electrons to achieve a noble gas configuration. This stable configuration is called an octet because it consists of 8 valence electrons (s p ), 2 from the outermost s orbital and 6 from the outermost p orbital. Oxygen has the electron configuration 1s 2s 2p . When oxygen reacts to form ionic compounds, it completes its octet by gaining two electrons from the element it reacts with. These two electrons add to the p orbital of oxygen, giving it the electron configuration (1s 2s 2p ) of neon.
In an ionic bond, oppositely charged ions are held together by the electronic force of attraction that exists between oppositely charged particles. In the ionic compound, anions and cations are present in a ratio that causes the total charge on the compound to be zero. Sodium phosphide, Na P, has three sodium ions for each phosphide ion. This ratio insures a zero total charge given the charges on the two individual ions (Na = 1 , P = 3-).
In this arrangement, like-charged ions are shielded from each other and electronic repulsion is reduced. Also, the force of attraction between oppositely charged ions is maximized. Each of these events contributes to a lowering of energy and an increase in stability of the ionic compound.
Explain how a pure metal is held together. Include a definition of a metallic bond in your explanation.
A piece of pure metal, such as copper or iron, consists not of metal atoms, but of closely packed cations. The cations are surrounded by mobile valence electrons that are free to drift from one part of the metal to another. Metallic bonds result from the attraction between the free-floating valence electrons and the positively charged metal ions.
Bond dissociation energy is the energy required to break a single bond. The greater the bond dissociation energy, the more stable the compound. Due in part to the high bond dissociation energy of carbon-carbon bonds, carbon compounds are not very reactive chemically.
Yes, sulfur and phosphorus can expand the octet. They can have 12 or 10 valence electrons, respectively, when combined with small halogens. In PCl , phosphorus has 10 valence electrons
Explain what is meant by VSEPR theory. Give an example of how VSEPR theory can be applied to predict the shape of a molecule.
VSEPR (valence-shell electron-pair repulsion) theory states that because electron pairs repel, molecules adjust their shapes so that the valence-electron pairs, both bonding and non-bonding, are as far apart as possible. Methane, CH , for example, has four bonding electron pairs and no unshared pairs. The bonding pairs are farthest apart when the angle between the central carbon and each of its attached hydrogens is 109.5 . This is the angle that is observed experimentally.
A polar molecule is one in which one end of the molecule has a slightly negative electric charge and the other end has a slightly positive electric charge. An example of a polar molecule is water. The oxygen atom in water develops a slightly negative charge and the hydrogen atoms develop slightly positive charges because of the difference in electronegativity between the oxygen and hydrogen atoms
What determines the degree of polarity in a bond? Distinguish between nonpolar covalent, polar covalent, and ionic bonds in terms of relative polarity.
The relative electronegativity of the two bonded atoms determines the polarity of a bond. If the difference in electronegativities between the two atoms is less than 0.4, the bond is nonpolar covalent. If the difference in electronegativities between the two atoms is 0.4 to 1.0, the bond is moderately polar covalent. If the difference in electronegativities between the two atoms is 1.0 to 2.0, the bond is highly polar covalent. If the difference in electronegativities between the two atoms is more than 2.0, the bond is ionic.
What are dispersion forces? How is the strength of dispersion forces related to the number of electrons in a molecule? Give an example of molecules that are attracted to each other by dispersion forces.

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Dispersion forces are the weakest of all molecular interactions, and are thought to be caused by the motion of electrons. Generally, the strength of dispersion forces increases as the number of electrons in a molecule increases. Diatomic molecules of halogen elements are an example of molecules whose attraction for one another is caused by dispersion forces.
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General Chemistry: Principles and Modern Applications11th EditionBissonnette, Herring, Madura, Petrucci
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