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    HonorsChemistry - Chapter 7.1

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    HonorsChemistry - Chapter 7.1

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    2 views23 pages

    HonorsChemistry - Chapter 7.1

    Uploaded by

    Hirana123

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    © All Rights Reserved
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    of 23

    Chapter 7.

    1
    Valence Electrons

    ● Elements within a group in a periodic table have similar properties because they gave
    same number of valence electrons.
    ● Valence electrons are involved in the formation of chemical bonds between two atoms.
    ● Recall that ions are formed when atoms gain or lose an electron and therefore have
    negative / positive charge.
    ● Octet Rule : Atoms tend to gain, lose or share electrons in order to acquire eight valence
    electrons
    ● Cation : A positively charged ion is called a cation
    ● Anion: A negatively charged ion is called an anion
    Chemical Bonds

    ● A Chemical bond is a force that holds two atoms together.


    ● Chemical Bonds can form by:
    ○ The attraction between the positive nucleus of one atom and the negative electrons of
    another atom.
    ○ The attraction between the positive and negative ions.
    Valence Electrons

    ● Electron dot structures is a type of diagram used to keep track of valence electrons.
    ● Electron dot structures are especially useful to illustrate the formation of chemical bonds.
    ● For example, carbon has electron configuration of 1s2 2s2 2p2. It has 4 valence electrons in the
    second energy level. These are represented by 4 dots around the symbol C in the table.
    Ionization Energy

    ● Ionization energy
    ○ the amount of energy that must be absorbed by an atom to discharge an electron to form a positive ion
    (cation).
    ○ It indicates how easily an atom loses its electron.
    ○ It is measured in KJ/mol.

    Mg + E -> Mg+ + e-
    Electron Affinity

    ● Electron Affinity
    ○ the amount of energy released when an electron is attached to a neutral atom to form a negative ion
    (anion).
    ○ It indicates how much attraction an atom has for electrons.
    ○ It is also measured in KJ/mol.
    Chemical Reactivity

    ● Noble gases have high ionization energy and low electron affinity therefore they lack
    chemical reactivity.
    ● Other elements in the periodic table react with each other forming numerous
    compounds.
    ● The difference in reactivity of elements is directly related to the valence electrons
    and the octet rule
    ● Octet - is the stable arrangement of 8 valence electrons in the outermost energy
    level.
    Chemical Reactivity

    ● Noble gases are unreactive


    ○ They have full outermost energy level with eight valence electrons (ns2np6)

    All other elements tend to react to acquire the stable electron structure of noble
    gas.
    Positive Ion Formation

    ● Positive ion is formed when an atom loses one or more valence electrons to attain a
    noble gas configuration.
    ● Cations carry positive charge because they have more protons compared to
    electrons.
    ● For example, Na with electron configuration 1s22s22p6 3s1, loses the valence
    electron in 3s subshell and attains the electron configuration of Ne (1s 22s22p6 )
    ● Although the Na+ ion has the same electron configuration of Ne, it is not Neon.
    ○ It is a Sodium ion with a single positive charge.
    ○ The 11 protons within the nucleus will still establish the character of Sodium in
    the Na+ ion.
    Metal Ions

    ● Metal atoms are very reactive as they lose their valence electrons easily.
    ● Group 1 and 2 metals are the most reactive metals in the periodic table
    ● Some group 13 atoms also form ions
    Transition Metal Ions

    ● Transition metals generally have a outer energy level of ns 2 and a partially or fully filled inner
    d subshell.
    ● They generally have 2 valence electrons (ns2)
    ● When forming cations, transition metals commonly lose their 2 valence electrons forming 2+
    ions.
    ● They may also lose d electrons to form ions 3+ or greater.
    ● It is difficult to predict the number of electrons that will be lost.
    ● For example, iron (Fe) forms both Fe2+ and Fe3+ ions.
    ● Rule of Thumb: Transition metals will form ions with 2+ or 3+ charge.
    Pseudo Noble Gas Configuration

    ● Octet (or) noble gas configuration


    ○ is the most stable electron configuration.
    ○ ns2np6
    ○ It has 8 valence electrons
    ● Pseudo Noble Gas Configuration is an electron configuration with fully filled s, p , d orbitals.
    ○ Offers relatively more stability.
    ○ Has (n-1)s2 (n-1)p6 (n-1) d 10 configuration
    ○ Has 18 valence electrons

    For example,
    ● Zn has electron configuration of 1s2 2s2 2p6 3s2 3p64s23d10.
    ● It has 2 valence electron in the 4th shell.
    ● If it loses the 2 valence electrons, it becomes Zn2+ with electron configuration 1s2 2s2 2p6 3s2
    3p63d10.
    ● Note that it has 18 valence electrons in the 3rd shell acquiring pseudo noble gas configuration.
    Negative Ion Formation

    ● Nonmetals easily gain electrons to attain a stable outer electron


    configuration.

    For example, Chlorine has configuration (Cl) : 1s22s22p63s23p5

    When Cl gains an electron, it becomes an anion and gets [Ar] configuration :


    (Cl-) 1s22s22p63s23p6

    Cl- is called Chloride ion.


    Anions

    Anion is a negatively charged ion.

    To designate an anion, the ending - ide is added to the name of the element.

    Chlorine - Chloride

    Fluorine - Fluoride

    Bromine ? Iodine? Nitrogen? Oxygen? Carbon? Iodine? Phosphorus?


    Energy Change

    ● When forming cations, an atom absorbs energy. Recall that ionization


    energy is added to the atom to discharge the electron.
    ● When forming anions, an atom releases energy to gain the electron.
    Nonmetal Ions

    ● Non metals gain the number of electrons required to achieve 8 valence


    electrons(octet).
    ● Some nonmetals can gain or lose electrons to form octet.
    ● For example, Phosphorus has electron configuration 1s22s22p63s23p3
    ○ It can gain 3 electrons (P3-)to achieve [Ar] configuration.1s22s22p63s23p6
    ○ It can lose 5 electrons (P5+)to achieve [Ne] configuration.1s22s22p6
    Nonmetal Ions

    ● In general, to achieve stable octet


    ○ Group 15 elements gain three electrons
    ○ Group 16 elements gain 2 electrons
    ○ Group 17 elements gain 1 electron
    Quiz
    Self Check Quizzes (mheducation.com)

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