CA Lesson 3 Periodic Trends PDF

Lesson 3 Periodic Trends  Focus Question How can you use the periodic table to predict an element's properties?  New Vocabulary ion ionization energy octet rule electronegativit y  Review Vocabulary principal energy level: the major energy level of an atom  Atomic...

Lesson 3 Periodic Trends  Focus Question How can you use the periodic table to predict an element's properties?  New Vocabulary ion ionization energy octet rule electronegativit y  Review Vocabulary principal energy level: the major energy level of an atom  Atomic Radius Atomic size is a periodic trend influenced by electron configuration.  Atomic Radius Atomic radius generally decreases from left to right within a period. Atomic radius generally increases as you Interpret Trends in Atomic Radii Use with Example Problem 2. SOLVE FOR THE UNKNOWN Problem Which has the largest atomic Determine the periods. radius: carbon (C), fluorine (F), From the periodic table, all the beryllium (Be), or lithium (Li)? elements are found to be in period 2. Answer without referring to Figure Apply the trend of decreasing radii 12 (slide 6). Explain your answer in across a period. terms of trends in atomic radii. Ordering the elements from left-to- Response right across the period yields: Li, Be, ANALYZE THE PROBLEM C, and F. You are given four elements. First, The first element in period 2, lithium, determine the groups and periods has the largest radius. the elements occupy. Then apply EVALUATE THE ANSWER the general trends in atomic radii to determine which has the largest The period trend in atomic radii has atomic radius. been correctly applied. Checking radii values in Figure 12 (slide 6) verifies the answer.  Ionic Radius An ion is an atom or bonded group of atoms with a positive or negative charge. When atoms form ions, they become charged, and their radius changes.  Ionic Radius When atoms lose electrons and form positively charged ions, they become smaller, for two reasons: The loss of a valence electron can leave an empty outer orbital, resulting in a smaller radius. Electrostatic repulsion decreases, allowing the electrons to be pulled closer to the nucleus. When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion. Ionic Radius  Ionic Radius The ionic radii of positive ions generally decrease from left to right. The ionic radii of negative ions generally decrease from left to right, beginning with group 15 or 16. Both positive and  Ionization Energy Ionization energy is defined as the energy required to remove an electron from a gaseous atom. The energy required to remove the first electron is called the first ionization energy. Removing the second electron requires more energy, which is called the second ionization energy. Each successive ionization requires more energy, but it is not a steady increase. Ionization Energy  Ionization Energy First ionization energy increases from left to right across a period. First ionization energy decreases down a group because atomic size increases, and less energy is required to remove an  Ionization Energy The octet rule states that atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons. The first-period elements and the second-period metals are an exception to the rule. They are stable when they have just 2 valence electrons, in the 1s orbital.  Electronegativity The electronegativity of an element indicates its relative ability to attract electrons in a chemical bond. Electronegativity decreases down a group and increases left to right across a period. Electronegativity  Quiz 1 How is the radius of a metal atom. measured? A the distance between two adjacent atoms in a crystal lattice B the distance between two identical atoms in a molecule C one-half the distance between two CORREC adjacent atoms in a crystal lattice T D one-half the distance between two identical atoms in a molecule  Quiz 2 Moving left to right within a period,. atomic radius generally ______. A stays the same B increases C decreases CORREC T D increases, then decreases  Quiz 3 Moving down within a group, atomic. radius generally ______. A stays the same B increases CORREC T C decreases D increases, then decreases  Quiz 4 Moving left to right within a period,. first ionization energy ______. A stays the same B increases C decreases CORREC T D increases, then decreases  Quiz 5 Atoms tend to gain, lose, or share. electrons in order to acquire how many valence electrons? A 0 B 6 C 8 CORREC T D 18