Chapter 5; Periodic Table; History of the Periodic Table

1868 & 1895, Helium.

1868, Helium = component of the sun based on emission spectrum of sunlight. 1895, Ramsay = Helium exists on Earth

How do the atomic numbers of the elements within each of the groups 1,2, and 13018 of the periodic table vary?

2-8-8-18-18-32-32

Actinides definition and location.

Actinides: 14 elements with atomic numbers from 90, Thorium, to 103, Lawrencium. Between Groups 3 and 4.

Definition of atomic radius? What is the periodic trend? Elements further left have what? So what happens to the nuclear charge on the electrons? How does that effect the electron cloud and the atomic radius? What is the group trend? Elements further down have what? How does that effect the electron cloud and the atomic radius?

Atomic radius is defined as 1/2 the distance between the nuclei of identical atoms that are bonded together. Periodic Trends: INcrease RIGHT - LEFT. Elements further left on the periodic table have fewer protons pulling on the same number of energy levels. This results in a less effective nuclear charge or pull on the electrons. Because the electrons are not being pulled as tightly or closely to the nucleus the electron cloud is expanded. Consequently the atomic radii of the element is larger than that of elements with fewer energy levels, elements further up a group. Group Trend: INcrease UP - DOWN Elements further down a group have more energy levels that are located further and further away from the nucleus. So the electron cloud is expanded. Consequently the atomic radii of the element is larger than that of elements with fewer energy levels, elements further up a group. (Shielding?)

Mendeleev - How did he establish credibility? What were the elements? What is he credited for?

But his procedure left empty spaces in his periodic table. He predicted the chemical properties of 3 of the spaces - they were later discovered as Scandium, gallium and germanium. His success earned him credibility as the discoverer of the periodic table.

Pattern of periodicity.

Differences in atomic number between groups 1, 2 and 13 to 18 are the same. 8 8, 18 18, 32.

Who discovered periodic law?

Dmitri Mendeleev

Horizontal arrangement of elements are called? How many periods are there in a periodic table? How is periodic length determined?

Elements organized horizontally across are called rows or periods. There are a total of 7 periods and a periods length is determined by the number of electrons that can occupy the sublevels in that period.

Reason of periodocity

Explained by arrangement of electrons around nucleus...section 2.

September 1860, FICC full form? Who? What did he do? What did that lead to?

First International Congress of Chemists. Stanislao Cannizzaro. Provided an accurate method for measuring atomic mass. Led to standard values and search for relationships between atomic mass and properties of elements

Who established atomic numbers as the basis for organizing the periodic table?

Henry Moseley

Define Ionization Energy? Period trend? Why(4sent.)? Compare nonmetals and metal ionization energy? Group Trend? Why (5sent)?

Ionization energy is the energy required to remove electrons from an atom. Periodic trend : INcrease LEFT - RIGHT Elements further left on the periodic table have fewer protons pulling on the same number of energy levels. This results in a less effective nuclear charge or pull on the electrons.The decreased nuclear pull on the electrons, especially the valance electrons, allows the atom to loose electrons with easier, with less energy, with less ionization energy. Nonmetals have a higher ionization energy than metals. Group Trend: INcrease DOWN -UP Elements further down a group have more energy levels that are located further and further away from the nucleus. The atoms of these elements have more electrons spread out over more energy levels between the nucleus and the the outer shell. This results in a more effective shielding of the nuclear charge or pull on the outer electrons. This results in electrons being held less tightly to the nucleus. As a result, it is easier for the atom to loose electrons.

Mendeleev - How did he organize? What did he notice? What did he create?

Mendeleev organized name of element, its atomic mass and physical and chemical properties on cards and arranged the cards looking for patterns. Noticed that if elements are ordered according to increasing atomic mass, there were similarities in chemical properties at regular intervals, there was a periodic pattern. He created the periodic table of elements.

1911, reason for element anomalies by Moseley. Worked with? Examined what? Saw what pattern? Led to what definition and what basis for organization?

Moseley, working with Rutherford, examined the spectra of 38 different metals and saw a pattern - they were organized better when arranged according to the number of protons in the nucleus. Led to definition of atomic number, and that the atomic number, not atomic mass, is the basis for organization.

Since then & Definition of the Periodic Table

New elements discoveries and creations. Periodic table : an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column or group.

Name the 3 sets of elements added to the periodic table after Mendeleev.

Noble Gases, Lanthanide and Actinide.

Why are noble gases stable? Why is helium stable? Why are other noble gases stable?

Noble gases are stable because they have special electron configurations. Helium is stable because its highest occupied level, the 1s orbital, is completely filled with electrons. All the other elements have stable octets in their highest occupied level.

Ramsay, new group, noble gases, location? 1898, names of 2 more noble gas discoveries? 1900, Who? Last noble gas?

Ramsay placed noble gas group between Group 17, the fluorine family, and Group 1, the lithium family. 1898, Krypton and Xenon. 1900, Dorn finds Radon.

Mendeleev- 2 remaining questions are?

Reasons for chemical periodicity and the existence of element anomalies that couldn't be arranged by increasing atomic mass.

Early 1900s, reason for difficultly in identifying Lanthanides? Lanthanide definition.

Similar chemical and physical properties made them difficult to separate and identify, needed lots of chemists. Lanthanides: 14 elements with atomic numbers from 58, Cerium, to 71, Lutetium.

Who is credited with developing the method that led to the determination of standard relative atomic mass?

Stanislao Cannizzaro

1894, Noble Gas: Which 2 scientists? Which gas was the 1st discovery? Reason for late discovery?

Strutt and Ramsay. Discovered Argon. Unnoticed because of its lacking chemical reactivity.

Block s elements are what kind of elements? Are group 1 or group 2 elements more reactive? Group 1 elements have what? How does that make them more reactive? What are Group 1 metals called? Name them? What 2 physical properties do they have? Are they found in nature, Why?What do they combine readily with? What do they strongly react with? What 2 things are produced in that reaction? So how are they stored? And elements lower on the group 1 metals have what?

The elements in the s block are chemically reactive metals. Group 1 metals are more reactive. The outermost energy level in an atom of each group 1 element contain 1s electron. For this reason, Group 1 metals can easily and readily loose this single electron, making them very reactive. The Group 1 elements are called alkali metals. Lithium, sodium, potassium, rubidium, cesium and francium. They each have a silvery appearance and are soft. They are not found in nature because of their high reactivity. They combine readily with nonmetals. They react strongly with water to produce hydrogen gas and an aqueous solutions of substances called alkalis. Because they are so reactive they are stored in kerosene. And elements lower in the group successively have lower melting temperatures.

What are group 2 elements called?Name them? What do tehy contain? How are they different physically.

The elements of group 2 are called alkaline earth metals. They are beryllium, magnesium, calcium, strontium, barium and radium. They contain 2 electrons in tehri outer most s sublevel. They are harder, denser and stronger than alkali metals. They have higher melting points. They are also too reactive to be found in nature as free elements.

State the Periodic Law

The physical and chemical properties of the elements are periodic functions of their atomic numbers. AKA when elements are arranged in order of increasing atomic number, elements of similar properties appear at regular intervals.

1960s Problems

learn properties of elements and compounds, no accurate method to determine element's atomic mass or the number of atoms of an element in a specific compound