Trends among elements in the periodic table include their sizes and their abilities to lose or attract electrons. Section 3: Periodic Trends K What I Know W What I Want to Find Out L What I Learned

5(C)Use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy. 2(H)Organize, analyze, evaluate, make inferences, and predict trends from data. 2(I)Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology-based reports. 3(A)In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. Periodic Trends Copyright © McGraw-Hill Education

Essential Questions What are the period and group trends of different properties? How are period and group trends in atomic radii related to electron configuration? Periodic Trends Copyright © McGraw-Hill Education

Review principal energy level Periodic Trends Copyright © McGraw-Hill Education Vocabulary New ion ionization energy octet rule electronegativity

Atomic Radius Periodic Trends Copyright © McGraw-Hill Education Atomic size is a periodic trend influenced by electron configuration. For metals, atomic radius is half the distance between adjacent nuclei in a crystal of the element.

Atomic Radius Periodic Trends Copyright © McGraw-Hill Education For elements that occur as molecules, the atomic radius is half the distance between nuclei of identical atoms that are chemically bonded together.

Atomic Radius Periodic Trends Copyright © McGraw-Hill Education Atomic radius generally decreases from left to right, caused by increasing positive charge in the nucleus. Valence electrons are not shielded from the increasing nuclear charge because no additional electrons come between the nucleus and the valence electrons. Atomic radius generally increases as you move down a group. The outermost orbital size increases down a group, making the atom larger.

Atomic Radius Periodic Trends Copyright © McGraw-Hill Education

Periodic Trends Copyright © McGraw-Hill Education Interpret Trends in Atomic Radii EVALUATE THE ANSWER The period trend in atomic radii has been correctly applied. Checking radii values in Figure 11 (slide 8) verifies the answer. Use with Example Problem 2. Problem Which has the largest atomic radius: carbon (C), fluorine (F), beryllium (Be), or lithium (Li)? Answer without referring to Figure 11 (slide 8). Explain your answer in terms of trends in atomic radii. Response ANALYZE THE PROBLEM You are given four elements. First, determine the groups and periods the elements occupy. Then apply the general trends in atomic radii to determine which has the largest atomic radius. SOLVE FOR THE UNKNOWN Determine the periods. From the periodic table, all the elements are found to be in period 2. Apply the trend of decreasing radii across a period. Ordering the elements from left-to-right across the period yields: Li, Be, C, and F. The first element in period 2, lithium, has the largest radius.

Ionic Radius Periodic Trends Copyright © McGraw-Hill Education When atoms lose electrons and form positively charged ions, they always become smaller for two reasons: 1.The loss of a valence electron can leave an empty outer orbital, resulting in a smaller radius. 2.Electrostatic repulsion decreases allowing the electrons to be pulled closer to the nucleus.

Ionic Radius Periodic Trends Copyright © McGraw-Hill Education When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion.

Ionic Radius Periodic Trends Copyright © McGraw-Hill Education 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 negative ions increase in size moving down a group.

Ionic Radius Periodic Trends Copyright © McGraw-Hill Education

Ionization Energy Periodic Trends Copyright © McGraw-Hill Education 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.

Ionization Energy Periodic Trends Copyright © McGraw-Hill Education

Ionization Energy Periodic Trends Copyright © McGraw-Hill Education Removing the second electron requires more energy, and is called the second ionization energy.

Ionization Energy Periodic Trends Copyright © McGraw-Hill Education 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 electron farther from the nucleus.

Ionization Energy Periodic Trends Copyright © McGraw-Hill Education The ionization at which the large increase in energy occurs is related to the number of valence electrons. 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 octet rule is useful for predicting what types of ions an element is likely to form.

Electronegativity Periodic Trends Copyright © McGraw-Hill Education 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.

Periodic Trends Copyright © McGraw-Hill Education Review Essential Questions What are the period and group trends of different properties? How are period and group trends in atomic radii related to electron configuration? Vocabulary ion ionization energy octet rule electronegativity