Presentation on theme: "To Bond or Not to Bond That’s the Question You can use the periodic table to determine the number of valence electrons. Group 1 has 1 valence electron."— Presentation transcript:
To Bond or Not to Bond That’s the Question You can use the periodic table to determine the number of valence electrons. Group 1 has 1 valence electron. Group 2 has 2 valence electrons Groups 3-12 do not have a rule relating their valence electrons to their group number. Groups 13-17 have 7or less valence electrons.
Not all atoms bond in the same way. Some don’t bond at all. The number of valance electrons determines whether or not they will bond. The noble gases (group 18) do not usually form chemical bonds. They already have 8 valence electrons. Their outermost energy level is considered full.
An atom with fewer than 8 valence electrons is much more likely to form bonds. Atoms gain, lose, or share electron in order to have a filled outermost energy level. There is an exception to this. Helium only needs only two valence electrons. Hydrogen and Lithium have one valence electron. Therefore, they bond by gaining, losing or sharing electrons to achieve 2 electrons in their first energy shell.
Sulfur has 6 valence electrons. It can have 8 by gaining 2 electrons or by sharing two electrons from other atoms.
Magnesium has 2 valence electrons. It can have a full outer level by losing 2 electrons. The second energy level becomes the outermost energy level and contains 8 electrons.
Ionic Bonds A bond that is formed when electrons are transferred from one atom to another atom. One or more valence electrons is transferred from one atom to another. The outermost energy levels of the atoms in the bonds are filled.
Charged Particles Ions are charged particles that are formed when an atom gains or loses electrons. An atom cannot gain electrons without another atom nearby to lose electrons or cannot lose electrons without a nearby atom to gain them.
Ionic bonds are formed when atoms pull electrons away from other atoms. Atoms that lose electrons now have fewer electrons than protons and now have a positive charge. Atoms of metals have few valence electrons so they tend to lose them and become positive ions.
Ionic Bond BBetween atoms of metals and nonmetals with very different electronegativity BBond formed by transfer of electrons PProduce charged ions all states. Conductors and have high melting point. EExamples; NaCl, CaCl 2, K 2 O
Sodium (Na) has only one valence electron. It can lose its 1 electron to another atom. The second energy level becomes its filled level. Now sodium has one more proton than electron so it has a positive charge. The sodium ion is 1+ charge and is written as Na +
Forming Negative Ions Some atoms gain electrons during chemical changes. When this happens, there are more electrons than protons thus forming a negative charge. Nonmetals gain electrons.
Oxygen has 6 valence electrons. It needs two more in order to fill its outermost shell. It will gain 2 electrons from another atom. Now the outermost energy level is filled. Since it has 2 more electrons than protons, it becomes an oxide ion that has a 2- charge. the symbol for the oxide ion is O 2-
-ide is used for the names of the negative ions formed when atoms gain electrons.
Covalent Bonding Forms when atoms share one or more pairs of electrons. Remember water? Oxygen has 6 valence electrons and needs 2 more. Hydrogen has 1 valence electron and need one more to have a full shell. So they share electrons.
Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles, they are not conductors at any state Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC
when electrons are shared equally NONPOLAR COVALENT BONDS H 2 or Cl 2
2. Ionic Bonds - Draw the Lewis structures for each atom, draw arrows to show the transfer of electrons, write the charge for each ion, and then write the chemical formula. (A)Potassium + Iodine (B) Magnesium + Oxygen (C) Lithium + Nitrogen
3. Covalent Bonds – Draw the Lewis structures for each atom, draw circles to show the electrons that are shared, and then write the bond structure and chemical formula. (A)Fluorine + Fluorine (B) 3 Hydrogen + 1 Phosphorus (C) 2 Hydrogen + 1 Sulfur