The Periodic TableThe Periodic Table

Objective #1: TSWBAT Explain the reason for creating a periodic table

1. Imagine if you were inside your favorite music store. If you noticed, the store has similar genre’s of music in the same aisle and different genre’s on other aisles.

2. Compare an organized music store to one that is in total disarray. Imagine the frustration you would have looking for the desired product.

3. Scientist had a similar problem. They had tons of different elements that were discovered but no one knew the relationship between these different elements. As a result, there was a need to organize these elements. They were later organized based on behavior and structure composition.

Objective #1: TSWBAT Explain the reason for creating a periodic table

4. Imagine the chaos that may have occurred if two people identified the same element but called it a different name. If there was no system of organization, would our understand of science have advanced?

5. There were many that attempted to organize the elements; however, it wasn’t until a Russian chemist by the name of Dmitri Mendeleev was in the process of creating a textbook for his students. He was trying to come up with a way to describe the 63 different elements. The result was the modern periodic table.

Assessment Question:

• What was the advantage of organizing the elements?

Objective #2: TSWBAT Use the scientific method to explain how Mendeleev created & designed the periodic table.  1. Observation: If you look at the current period table, we notice that

each of these elements has a relationship with one another. 2. Hypothesis: If there is a relationship between the different

elements, then the elements can be grouped together based on common properties

Objective #2: TSWBAT Use the scientific method to explain how Mendeleev created & designed the periodic table.

3. Gather Evidence: – While playing a game of solitaire Mendeleev noticed that all of

the elements had certain properties in common similar to the different suits in the card game.

– Mendeleev noticed that each of the elements different by their atomic mass. His initial draft contained a version based on mass.

– Later, it was noticed that different groups of elements shared the same number of “valence electrons.” Valence electrons are the electrons in the outermost orbital. To understand this concept, students will need to refer back to Bohr’s model of the atom.

– Those with similar valence electrons vary by mass– If you also notice, all the elements vary by 1 proton

Objective #2: TSWBAT Use the scientific method to explain how Mendeleev created & designed the periodic table.

4. Conclusion: The elements were organized successfully into categories thus the initial adaptation or draft of the periodic table was born in 1869.

 5. Theory: When elements share similar properties, they

can be arranged based on certain properties. The modern periodic table proves this theory.

Assessment Question:

• What is meant by the term valence electrons?

Objective # 3: TSWBAT Explain periodic law

• The periodic law is self-explanatory;.– It is the law that governs the behavior of the modern periodic

table. – When Mendeleev “first” designed the periodic table he was not

aware of Bohr’s model of the atom, meaning he did not know about protons nor did he know that atoms of the same element had the same number of protons and atoms of different elements have a different number of protons.

– Therefore, the modern periodic table is now arranged based on atomic number.

1. The periodic table was broken down into periods and groups

2. Periods are counted from top to bottom. We have 7 periods.

3. Periods are read from left to right4. Groups are counted from left to right. We have 18 groups5. Groups are read from top to bottom

Assessment Question

• How many periods are there on the periodic table? Groups?

Objective #4: Understand the components of the periodic table

1. Atomic Number: It will equal the number of protons in an element. To find the Atomic number, simply count the elements on the periodic table till you get to the one you want. Read from left to right.

2. Mass Number: sum of protons and neutrons (Understand concept only)

3. Isotopes p117: Same atomic number (# of protons) but different mass numbers because of the # of neutrons. O-16; O-17; & O-18 are examples of Isotopes. They are essentially the same element.

Objective #4: Understand the components of the periodic table

• There are five classes of elements: metals, nonmetals, metalloids, transition metals & noble gases– A metal is a chemical element whose atoms readily

lose electrons to form positive ions– A transition metal is any of the metallic elements

within Groups 3 to 12 in the Periodic Table that have an incomplete inner electron shell.

– A nonmetal is any of a number of elements, such as oxygen or sulfur, that lack the physical and chemical properties of metals

– A metalloid is an element that has properties of both a metal and a nonmetal

– A noble gas is a an element with a complete octet shell. These are your most stable elements.

Objective #4: Understand the components of the periodic table

Family Name

Group

Family Name Group

Alkali Metals 1 Nitrogen Family 15

Alkaline Earth Metals

2 Oxygen Family 16

Transition Metals

3-12 Halogens 17

Boron Family 13 Noble Gases 18

Carbon Family

14

Objective #5: TSWBAT Understand the periodic trends

• You can count the number of valence electrons by placing your hand over the metalloids and counting from left to right. The maximum number of valence electrons is eight.

• Since eight electrons are the maximum amount of electrons those with eight are considered stable and are the least reactive.

• Every element desires to get eight electrons. They usually obtain this by forming a compound.

Objective #5: TSWBAT Understand the periodic trends

• As you go down the groups, the weight of each element increases and the strength of each element also increases.

• The most reactive metals are on the left side of the chart. The most reactive non-metals are on the right side of the charge excluding noble gases.

• If you place your hand in the center of the periodic table, elements in the center become more metallic from center to the left and more non-metallic from the center to the right.

Objective #5: TSWBAT Understand the periodic trends….

• Ionization Energy is defined as the energy required to remove an electron from a neutral atom or ion.

• This is always an endothermic process.• Ionization energy increases as you go from left to right• Ionization energy decreases going down a group• There are two types of ions (charged particles: Cations (+)

and Anions (-)

Objective #5: TSWBAT Understand the periodic trends….

1. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons

2. Elements are more reactive as you go down each group

3. In groups, reactivity of metals increases with atomic number because the ionization energy decreases & reactivity of non-metals decreases when atomic number increases because the electronegativity decreases.

4. In periods, reactivity of metals decreases when atomic number increases because the ionization energy increases. & reactivity of non-metals increases with atomic number because the electronegativity increases.

Miscellaneous information regarding the periodic table.

• Mendeleev did not know about protons• Mendeleev knew that all atoms of an element

have the same number of protons.• Mendeleev was the first to offer the best

explanation for how the properties of an element were related to its location on the periodic table.

• Helium is an exception to the octet rule. It only has 2 valence electrons but it is a stable gas.

Objective #6: Understand the different diagrams used to explain electron configuration

Electron Dot Diagram • The electron dot diagram is a model of an atom in

which a dot represents valence electrons. • The element symbol is placed in the middle to

represent the nucleus of that particular atom

He

• Therefore Helium would have 2 dots around it

• When drawing the dots, you draw them in clockwise fashion.

Assessment Question:• Create an electron dot diagram

for the following elements, Li, O, As, Si, I,

Lewis Structure• This structure replaces the dots with lines• A line represents two dots.

Objective 6: Understand the concept of electron configuration

• Everything in life wants to be at the lowest energy level. When describe electrons reaching this lowest energy, we define them as reaching “ground state” configuration

• Electrons in the nucleus arrange themselves to b in the lowest energy state

• The arrangement is known as electron configuration

• The electron configuration of an atom is a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels. 

Electronic Configuration Continued• There are three rules we use to determine electron

configuration– Aufbau principle (p133) – electrons occupy the

orbital with the lowest energy level first– Pauli’s exclusion principle – To occupy the same

orbital, two electrons must have opposite spins (clockwise/counterclockwise)

– Hund’s rule – one electron enters each orbital first and returns back to the initial orbital pairing with opposite spins.

Electronic Configuration Continued

– Based on your understanding of orbitals, we know how many electrons each orbital can hold.

– We also know that each element desires stability, 8e- with the exception of He that desires 2e-

– Elements that have not reached this complete set of valence electrons tend to be more reactive.

– When we discuss electron configuration we are simply explaining the arrangement of the electrons.

Electronic Configuration Continued• You write the e- configuration as follows: Period # ;

Orbital ; # of e- (written in superscript)– There is an exception to this rule, the d -orbital

shifts upwards a period.– The d-orbital starts at period three and not four as

listed on the table. They are placed in the 4th period because of their atomic numbers.

– Example, the electron configuration for Helium would be 1s2; Neon would be 1s2, 2s2, 2p6

• You can also write the configuration using the closest noble gas as your landmark and continue your configuration from the landmark. Example: [He]2s1