Why atoms form chemical bonds Electrons are in energy levels around the nucleus (electron cloud). The higher the energy level, the more energy is required for an electron to occupy that part of the cloud. The outermost part of the electron cloud contains the valence electrons – that is the valence shell. Maximum number of valence electrons in an atom is 8.
Atoms are stable when they have 8 valence electrons. When the atoms have 8 electrons, it is called an octet . Atoms must lose, gain or share electrons to attain the octet. Atoms that form bonds with other atoms by sharing them or transferring them is known as the Octet Rule .
There is always an exception! Hydrogen and Helium Hydrogen needs only one more to fill its valence shell. Helium has a full valence shell – it is stable and does not bond with other atoms.
So what about Lithium? Is it easier for Lithium to gain 7electrons or lose 1 electron?
Bond…. Chemical Bonds Ionic Bonds They are formed when atoms gain or lose electrons. If the compound has a metal, then it is an ionic bond. Ex. xx Na Cl x x x xx
When it loses 1 Ionization electron to become more stable, it has 11 protons (+) and When atoms gain 10 electrons (-) and or lose an electron, has a +1 charge. Cl has 17 protons. they become an When Cl gains 1 ion. electron to complete A Na atom has 11 the octet, it has 17 positively charged protons (+) and 18 protons and 11 electrons (-). negatively charged It is now an ion with electrons. a –1 charge.
Opposites Attract Since the Na has a + charge and the Cl has a – charge, the two atoms are attracted together and form an ionic bond. They have a 1:1 ratio when they combine…..
Covalent Bonds Atoms that share electrons form covalent bonds. If the atoms have a covalent bond and are the same type of atom…. They are diatomic molecules. Ex. xx xx x x Cl Cl xx x x x x xx
Metallic Bonding Metallic bonds - electrons are distributed equally through a metallic crystal. The electrons in metals can be thought of as being property of all the atoms. The positive nuclei are surrounded by a "sea of electrons" that are all attracted by the nuclei at the same time.
So you ask…. “How do I know if it is covalent or ionic?” Ionic bonds are formed by the attraction of two oppositely charged particles. Covalent bonds are formed when atoms share electrons. Typically bonds between metals and nonmetals form ionic bonds. Bonds between two nonmetals form covalent bonds.
Isn’t it ionic, don’t you think Electron pairs sometimes share unequally in covalent bonds. The attraction an atom has for the shared pair of electrons in a covalent bond is called electronegativity .
High Electronegativity (need to gain electrons) Low Electronegativity Atoms in Column 17 (need to lose have high electrons) electronegativity. Atoms in Columns 1 and 2 have low electronegativity. Cl F Br H K Li