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Explore the concept of chemical bonds, including covalent and ionic bonds, electronegativity, electron configurations, and structures of ionic compounds. Test your knowledge with a quiz!
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12.1 Section A and B, 12.2 Group 1 Period 6
Bonds • Bond – a force that holds together two or more atoms and functions as one unit • Bond energy – the strength required to break the bond
Example • What’s the difference between bond and bond energy?
Answer • Bonds hold together atoms while bond energy is a characteristic of a bond in which it describes how strong a bond is.
Types of Chemical Bonds • Covalent bond – a bond that forms when two nonmetals react • Ionic bond – a bond that forms when a nonmetal and a metal react • Polar Covalent bond – between two extremes in which atoms are not that different so that there is an unequal sharing of electrons
Example • What happens to the electrons in a covalent bond?
Answer • The electrons are shared by each of the atoms.
Electronegativity • Electronegativity – the ability for an atom to attract electrons • Electronegativity increases up a group and across a period • Similar electronegativity results in a covalent bond and different electronegativity results in an ionic bond • Electronegativity ranges from 0-4.0
Example • On the periodic table, how does electronegativity increase and decrease?
Answer • Electronegativity increases going up a group and across a period(left to right). It decreases going down a group and across a period (right to left).
Electron Configurations • Groups 1 and 2 are the s orbitals – two electrons max in each • Groups 3-12 are the d orbitals – 10 electrons max • Groups 13-18 are the p orbitals – 6 electrons max • Lanthanides – bottom of the periodic table – have f orbitals and hold 15 electrons • You read across the table to do electron configurations
Example • Write the electron configuration for Ca. Tell what noble gas you would use to abbreviate.
Answer • 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 • You would use Argon
Structures of Ionic Compounds • When a nonmetal and a metal react they usually form an octet (8 valence electrons) • Stable compounds achieve an octet • Cation is always smaller than the atom and the anion is always bigger than the atom • Cations are the metals and the anions are the nonmetals • Anions are bigger because they are greedy for electrons while the cation are smaller because they have to give up electrons • Polyatomic ions are held together by covalent bonds
Example • When a metal and a nonmetal react, in what conditions are they stable?
Answer • When they form an octet they are stable because they have achieved a noble gas electron configuration.
Quiz • What are cations? Anions? • What happens when a metal loses all of its valence electrons • What are the individual polyatomic ions held together by? • What is larger the anion or the cation? • What is the range of electronegativity?
Answers • Cations are the metals and the anions are the nonmetals. • It gets smaller because it loses its electrons. • Covalent bonds. • The anions are always bigger because they gain electrons from the metals. • The lowest electronegativity is 0 and the highest is 4.0.
References subtopic 1 http://www.vias.org/feee/img/00257.pngsubtopic 2 http://www.windows.ucar.edu/physical_science/chemistry/ch4_molecule_big.gifsubtopic 3 http://www.chem.fsu.edu/chemlab/chm1050lmanual/halogens/polar_bond.jpgsubtopic 4 http://www.mpcfaculty.net/mark_bishop/periodic_table_blocks_alone.jpgsubtopic 5 http://www4.nau.edu/meteorite/Meteorite/Images/Sodium_chloride_crystal.png
