The Periodic Table and Periodic Law

Transcription

1 The Periodic Table and Periodic Law Periodic trends in the properties of atoms allow us to predict physical and chemical properties. Section 1: Development of the Modern Periodic Table Section 2: Classification of the Elements Section 3: Periodic Trends Section 1: The periodic table evolved over time as scientists discovered more useful ways to compare and organize the elements. Section 2: Elements are organized into different blocks in the periodic table according to their electron configurations. Section 3: Trends among elements in the periodic table include their sizes and their abilities to lose or attract electrons. How was the periodic table developed? What are the key features of the periodic table? Why do elements in the same group have similar properties? Based on their electron configurations, what are the four blocks of the periodic table? What are the period and group trends of different properties? How are period and group trends in atomic radii related to electron configuration? 1

2 Vocabulary atomic number valence electron principal energy level New periodic law group period representative element transition element metal alkali metal alkaline earth metal New continued transition metal inner transition metal lanthanide series actinide series nonmetal halogen noble gas metalloid ion ionization energy octet rule electronegativity Section 1: Development of the Modern Periodic Table The periodic table evolved over time as scientists discovered more useful ways to compare and organize the elements. How was the periodic table developed? What are the key features of the periodic table? Vocabulary atomic number New periodic law group period representative element transition element metal alkali metal New continued alkaline earth metal transition metal inner transition metal lanthanide series actinide series nonmetal halogen noble gas metalloid Copyright McGraw-Hill Education Development of the Modern Periodic Table 2

3 Development of the Periodic Table In the 1700s, Lavoisier compiled a list of all the known elements of the time. Development of the Periodic Table The 1800s brought large amounts of information and scientists needed a way to organize knowledge about elements. John Newlands proposed an arrangement where elements were ordered by increasing atomic mass. Development of the Periodic Table Newlands noticed when the elements were arranged by increasing atomic mass, their properties repeated every eighth element. Development of the Periodic Table Meyer and Mendeleev both demonstrated a connection between atomic mass and elemental properties. Moseley rearranged the table by increasing atomic number, and resulted in a clear periodic pattern. Periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number is called periodic law. 3

4 The Modern Periodic Table The modern periodic table contains boxes that contain the element's name, symbol, atomic number, and atomic mass. The Modern Periodic Table Columns of elements are called groups. Rows of elements are called periods. Elements in groups 1,2, and possess a wide variety of chemical and physical properties and are called the representative elements. Elements in groups 3 12 are known as the transition metals. The Modern Periodic Table Elements are classified as metals, nonmetals, and metalloids. Metals are elements that are generally shiny when smooth and clean, solid at room temperature, and good conductors of heat and electricity. Alkali metals are all the elements in group 1 except hydrogen, and are very reactive. Alkaline earth metals are in group 2, and are also highly reactive. 4

5 The Modern Periodic Table The transition elements are divided into transition metals and inner transition metals. The two sets of inner transition metals are called the lanthanide series and actinide series and are located at the bottom of the periodic table. The Modern Periodic Table Nonmetals are elements that are generally gases or brittle, dull-looking solids, and poor conductors of heat and electricity. Group 17 is composed of highly reactive elements called halogens. Group 18 gases are extremely unreactive and commonly called noble gases. Metalloids, such as silicon and germanium, have physical and chemical properties of both metals and nonmetals. The Modern Periodic Table How was the periodic table developed? What are the key features of the periodic table? Vocabulary periodic law group period representative element transition element metal alkali metal alkaline earth metal transition metal inner transition metal lanthanide series actinide series nonmetal halogen noble gas metalloid 5

6 Section 2: Classification of the Elements Elements are organized into different blocks in the periodic table according to their electron configurations. Why do elements in the same group have similar properties? Based on their electron configurations, what are the four blocks of the periodic table? Vocabulary valence electron Organizing the Elements by Electron Configuration Recall electrons in the highest principal energy level are called valence electrons. All group 1 elements have one valence electron. 6

7 Organizing the Elements by Electron Configuration Group 2 elements have two valence electrons. The number of valence electrons for elements in groups is ten less than their group number. The energy level of an element s valence electrons indicates the period on the periodic table in which it is found. The s-, p-, d-, and f-block Elements The shape of the periodic table becomes clear if it is divided into blocks representing the atom s energy sublevel being filled with valence electrons. The s-, p-, d-, and f-block Elements s-block elements consist of group 1 and 2, and the element helium. Group 1 elements have a partially filled s orbital with one electron. Group 2 elements have a completely filled s orbital with two electrons. The s-, p-, d-, and f-block Elements Groups fill the p orbitals. In group 18, both the s and p orbitals of the period s principal energy level are completely filled. 7

8 The s-, p-, d-, and f-block Elements The d-block contains the transition metals and is the largest block. There are exceptions, but d-block elements usually have filled outermost s orbitals, and filled or partially filled d orbitals. The five d orbitals can hold 10 electrons, so the d-block spans ten groups on the periodic table. The s-, p-, d-, and f-block Elements The f-block contains the inner transition metals. f-block elements have filled or partially filled outermost s orbitals and filled or partially filled 4f and 5f orbitals. The 7f orbitals hold 14 electrons, and the inner transition metals span 14 groups. Why do elements in the same group have similar properties? Based on their electron configurations, what are the four blocks of the periodic table? Section 3: Periodic Trends Trends among elements in the periodic table include their sizes and their abilities to lose or attract electrons. 8

9 What are the period and group trends of different properties? How are period and group trends in atomic radii related to electron configuration? Vocabulary principal energy level New ion ionization energy octet rule electronegativity Atomic Radius 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 For elements that occur as molecules, the atomic radius is half the distance between nuclei of identical atoms that are chemically bonded together. 9

10 Atomic Radius 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 Ionic Radius 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 When atoms gain electrons, they can become larger, because the addition of an electron increases electrostatic repulsion. 10

11 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. Ionic Radius Both positive and negative ions increase in size moving down a group. Ionization Energy 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. 11

12 Ionization Energy Removing the second electron requires more energy, and is called the second 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 electron farther from the nucleus. Ionization Energy 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 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. 12

13 Electronegativity 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 13