Chapter 6 The Periodic Table

Organizing the Elements 6.1

Searching for an Organizing Principle Key Question How did chemists begin to organize the known elements? They used the properties of elements to sort them into groups. J.W. Dobereiner was a German chemist that published a classification system, in which the known elements were grouped in triads Triad is a set of three elements with similar properties

Mendeleev’s Periodic Table Key Question How did Mendeleev organize his periodic table? He arranged the elements in order of increasing atomic mass. Dmitri Mendeleev published his periodic table around the same time as Lothar Meyer (German chemist); these periodic tables were identical, but because Mendeleev published his table first and was able to explain its periodic trends better his was given the credit.

Today’s Periodic Table Key Question How is the modern periodic table organized? Increasing atomic number Henry Moseley determined an atomic number for each known element Groups are vertical Periods are horizontal Each period corresponds to a principal energy level

Periodic law is when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties Elements that are in the same group have similar chemical and physical properties

Metals, Nonmetals, and Metalloids Scientists must agree on a standard that will be used for communication purposes, these standards are set by IUPAC (International Union of Pure and Applied chemistry) They numbered the groups from left to right, 1-18

Key Question What are three broad classes of elements Key Question What are three broad classes of elements? Metals, nonmetals, and metalloids

Metals Most elements are metals Metals are generally good conductors of heat and electricity All metals are solids at room temperature, except Hg Many metals are ductile, and most are malleable

Nonmetals Most nonmetals are gases at room temperature There is a greater variation in the properties of nonmetals than in metals Nonmetals are poor conductors of heat and electricity, with an exception of carbon Solid nonmetals tend to be brittle

Metalloids Dark line separates the metals from the nonmetals, the elements along this border are called metalloids Metalloids may have properties similar to those of metals and nonmetals (depends on the condition)

Using the Periodic Table to Determine States of Matter Everything on the periodic table are solids (black), except the following: Hg and Br, which are liquids (dark blue) Diatomic molecules are gases, except Br (liquid) and Iodine (solid) Noble gases are gases (light blue)

PRACTICE Using the Periodic Table to Determine States of Matter: You have 2 minutes: Ti Br Ne C Hg S

Classifying the Elements 6.2

Reading the Periodic Table Key Question What information can be displayed in a periodic table? The symbols and names of the elements, along with information about the structure of their atoms. Group 1A elements are called alkali metals Group 2A elements are called alkaline-earth metals Group 7A (nonmetals) are called halogens

Electron Configurations in Groups Key Question How can elements be classified based on electron configurations? Noble gases, representative elements, transition elements, or inner transition metals

The Noble Gases Group 8A elements are called noble gases Sometimes called inert gases because they are stable and rarely take part in a reaction The highest occupied energy level for each element is completely filled with electrons; therefore, they are stable

The Representative Elements The elements in groups 1A-7A are called the representative elements They display a wide range of properties These elements may be metals, nonmetals, or metalloids The s and p sublevels of the highest occupied energy level are not filled

Transition Elements Transition metals are the group B elements that are usually displayed in the main body of a periodic table The highest occupied s sublevel and a nearby d sublevel contain electrons These elements are characterized by the presence of electrons in the d orbitals Inner transition metals are the elements that appear below the main body of the periodic table The highest occupied s sublevel and a nearby f sublevel generally contains electrons They are characterized by the presence of electrons in the f orbitals Were once referred to as rare-earth metals, but was misleading because some inner transition metals are more abundant than other elements

Blocks of Elements The s block contains the elements in groups 1A and 2A, and the noble gas helium The p block contains the elements in groups 3A-8A, except helium The transition metal blocks belong to the d block One less than the period number The inner transition metals belong to the f block Two less than the period number You are not required to know this way, but it wouldn’t hurt to know how because its shorthand!

Periodic Trends 6.3

What are the trends among the elements for atomic size? Trends in Atomic Size Atomic radius is one half the distance between the nuclei of two atoms of the same elements when the atoms are joined Key Question What are the trends among the elements for atomic size? Atomic size increases from top to bottom within a group, and decreases from left to right across a period

In Chapter 7, you will learn how ions are formed! Ion is an atom or group of atoms that has a positive or negative charge Atoms are electrically neutral because it has equal numbers of protons and electrons Key Question How do ions form? When electrons are transferred between atoms. An ion with a positive charge is called a cation An ion with a negative charge is called an anion In Chapter 7, you will learn how ions are formed!

Trends in Ionization energy Ionization energy is the energy required to remove an electron from an atom Key Question What are the trends among the elements for first ionization energy? Decrease from top to bottom within a group and increase from left to right across a period.

Trends in Ionic Size Key Question What are the trends among the elements for ionic size? Increase from top to bottom within a group. Generally, the size of cations and anions decrease from left to right across a period.

Trends in Electronegativity Electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound Key Question What are the trends among the elements for electronegativity? Values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.