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Chemical Bonds

Chemical Bonds. IONIC BONDING. Chemical properties, like reactivity, depend on e- configuration When highest occupied energy level is filled, atom is STABLE and not likely to react… called the OCTET rule Noble gases. ELECTRON SHELLS. Atomic number = number of Electrons

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Chemical Bonds

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  1. Chemical Bonds

  2. IONIC BONDING • Chemical properties, like reactivity, depend on e- configuration • When highest occupied energy level is filled, atom is STABLE and not likely to react… called the OCTET rule • Noble gases

  3. ELECTRON SHELLS • Atomic number = number of Electrons • Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. • Electron shells determine how an atom behaves when it encounters other atoms

  4. Electrons are placed in shells according to rules: • The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

  5. Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons Gain 4 electrons • C would like to • N would like to • O would like to Gain 3 electrons Gain 2 electrons

  6. Why are electrons important? • Elements have different electron configurations • different electron configurations mean different levels of bonding

  7. ELECTRON DOT CONFIGURATION • Model of atom in which dots represent valence e-

  8. Stable Electron Configurations

  9. CHECK YOUR UNDERSTANDING A. X would be the electron dot formula for 1) Na 2) K 3) Al   B.  X  would be the electron dot  1) B 2) N 3) P C. Draw the electron dot diagram for: BeOBrMgAlH

  10. IONIC BONDS • Atoms want to have a complete set of valence e-… they tend to react • Some achieve stable e- configurations thru transfer of e- between atoms

  11. TRANSFER OF e- • When elements react with each other, they sometimes transfer e- • Na + Cl • p no longer = e, so it’s not neutral • ION – atom that has + or - charge • Represented w/ + or – • When atom gains e-, it becomes – • When atom loses e- , it becomes +

  12. ANION - atom with negative charge • Named by adding –ide to end • Cl- = chloride • CATION – atom with positive charge • Named by just using element name with “ion” • Na+ - sodium ion

  13. LET’S PRACTICE NAMING IONS • Fluorine has __ valence electrons. It will (gain or lose) ___ e-, & becomes a (cation or anion) which is ( + or -) charge. Its name becomes _______. • Calcium has __ valence electrons. It will (gain or lose) ___ e-, & becomes a (cation or anion) which is ( + or -) charge. Its name becomes _______.

  14. Cesium has __ valence electrons. It will (gain or lose) ___ e-, & becomes a (cation or anion) which is ( + or -) charge. Its name becomes _______. • Oxygen has __ valence electrons. It will (gain or lose) ___ e-, & becomes a (cation or anion) which is ( + or -) charge. Its name becomes _______.

  15. PRACTICE NAMING IONS • Na + - Is this a cation or anion? What is its name? • N- - Is this a cation or anion? What is its name? • Beryllium --- Does it gain or lose electrons? How many? What charge does it become? Is it a cation or anion?

  16. CHECK YOUR UNDERSTANDING • What is an ionic bond? • What is an ion? • Cation? • Anion? • Name these ions: Li, Mg, O, S

  17. WRITE THESE ON YOUR PERIODIC TABLE

  18. FORMATION OF IONIC BOND • Remember, + attracts – • Chemical Bond – force that holds atoms or ions together as a unit • Ionic Bond – force that holds cations and anions together - Formed when e- transferred

  19. TURN TO PAGE 160 IN TEXT • Do the Data Analysis

  20. Ionic Bonds This table shows the atomic radius and ionic radius for six metals and six nonmetals. You will use the data to relate the size of an element’s atoms to the element’s location on the periodic table and to compare the sizes of atoms and their ions.

  21. Ionic Bonds • Using TablesWithin a period, what happens to the atomic radius as the atomic number of the elements increases?

  22. Ionic Bonds • Using TablesWithin a period, what happens to the atomic radius as the atomic number of the elements increases? Answer: Within a period, the atomic radius decreases as the atomic number increases.

  23. Ionic Bonds • Using TablesWithin Groups 1A, 2A, 6A, and 7A, what happens to the atomic radius of elements as the atomic number increases?

  24. Ionic Bonds • Using TablesWithin Groups 1A, 2A, 6A, and 7A, what happens to the atomic radius of elements as the atomic number increases? Answer: Within these groups, the atomic radius increases as the atomic number increases.

  25. Ionic Bonds • InferringHow does adding an occupied energy level affect the atomic radius? (Hint: Lithium is a Period 2 element and sodium is a Period 3 element.)

  26. Ionic Bonds • InferringHow does adding an occupied energy level affect the atomic radius? (Hint: Lithium is a Period 2 element and sodium is a Period 3 element.) Answer: When the next higher energy level is occupied, there is a significant increase in atomic radius.

  27. Ionic Bonds • Comparing and ContrastingCompare the atomic and ionic radii for potassium (K), and for bromine (Br).

  28. Ionic Bonds • Comparing and ContrastingCompare the atomic and ionic radii for potassium (K), and for bromine (Br). Answer: The ionic radius for potassium is much smaller than its atomic radius. The ionic radius for bromine is much larger than its atomic radius.

  29. Ionic Bonds • Making Generalizations What happens to the radius of an atom when the atom loses electrons? When the atom gains electrons?

  30. Ionic Bonds • Making Generalizations What happens to the radius of an atom when the atom loses electrons? When the atom gains electrons?Answer: With the loss of valence electrons, the radius decreases. With the addition of valence electrons, the radius increases.

  31. Ionic Bonds • Relating Cause and Effect Explain the difference in size between a metal atom and its cation.

  32. Ionic Bonds • Relating Cause and Effect Explain the difference in size between a metal atom and its cation. Answer: An energy level that was occupied is no longer occupied, and the size decreases.

  33. IONIZATION ENERGY • When atoms absorbs energy, e- can move to higher energy level • Ionization Energy – amt energy used to remove e- so it can overcome the attraction to the p • Lower ionization energy = easier to remove e- • Fig. 3 pg. 161 – Trends SUMMARIZE IT

  34. Ionic Bonds This figure shows two trends for ionization energy.

  35. CHECK YOUR UNDERSTANDING • For each of the following sets of atoms, decide which has the highest and lowest ionization energies and why. • a.  Mg, Si, S • b.  Mg, Ca, Ba • c.  F, Cl, Br

  36. IONIC COMPOUND Compound- substance made of 2 or more elements & can be broken down into those elements Chemical formula – notation that shows what elements a compound contains & the ratio of atoms or ions NaCl ( pg. 161) MgCl2

  37. Ionic Compounds What is the chemical formula for magnesium chloride?

  38. A magnesium atom cannot reach a stable electron configuration by reacting with just one chlorine atom. It must transfer electrons to two chlorine atoms. After the transfer, the charge on the magnesium ion is 2+ and its symbol is Mg2+.

  39. Ionic Compounds The formula for magnesium chloride is MgCl2. The 2 written to the right and slightly below the symbol for chlorine is used to show the relative numbers of atoms of the elements present. Magnesium chloride is used to control dust on unpaved roads.

  40. PROPERTIES OF IONIC COMPOUNDS • All ionic compounds form crystals • High melting points (800° C) • In solid state, poor conductor of electricity • When melted or dissolved in water, good conductor • Very hard & very brittle • Properties explained by strong attractions among ions in a crystal lattice

  41. Assessment Questions • When is an atom stable? • when its electrons are evenly distributed through its energy levels • when its lowest occupied energy level is filled with electrons • when its highest unoccupied energy level is filled with electrons • when its highest occupied energy level is filled with electrons

  42. Assessment Questions • Which description applies to an element that has two valence electrons? • reactive metal • nonreactive metal • reactive nonmetal • nonreactive nonmetal

  43. Assessment Questions • How do sodium and chlorine both achieve stable electron configurations when they react? • An electron is transferred from the sodium atom to the chlorine atom. • An electron is transferred from the chlorine atom to the sodium atom. • Both atoms gain one electron. • Both atoms lose one electron.

  44. Assessment Questions • Why do ionic compounds tend to have high melting points? • Ionic compounds contain more than one element, which causes a high melting point. • Ionic compounds cannot absorb energy efficiently because they contain ions. • An ionic compound contains metal atoms that raise its melting point. • A strong electrical attraction means ions require a lot of energy to move apart.

  45. Assessment Questions • Why do ionic compounds tend to have high melting points? • Ionic compounds contain more than one element, which causes a high melting point. • Ionic compounds cannot absorb energy efficiently because they contain ions. • An ionic compound contains metal atoms that raise its melting point. • A strong electrical attraction means ions require a lot of energy to move apart.ANS: D

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