Unit 1, Chapter 1: Elements and the Periodic Table Flashcards
Describe two significant differences between the Thomson model of the atom and the Rutherford model.
In the Rutherford model, the positive charge resides in a small space in the center of the atom, whereas in the Thomson model, the positive charge is everywhere.
Draw Lewis diagrams of lithium, carbon, and fluorine.
Lithium: ‘Li’ in the center with one electron above it
Carbon: ‘C’ in the center with two electrons above it, two below it, two to the right, and one to the left.
What information shows that the Bohr model of the atom and the electron cloud model are related?
Schrodinger’s calculation for the average distance between the nucleus and electron is the same as the radius Bohr calculated for the electron’s orbit.
Models are used in many areas of science. Why do you think that models are a very important tool for studying the atom?
Chemists use models to anticipate and predict the way something may behave. Because of this, chemists can use models to help explain, understand, and share certain concepts and information.
Describe one feature of Dalton’s model, the Thomson model. and the Bohr model that correctly describes one or more properties of the atom.
Dalton’s rules indicate that all matter consists of tiny particles (called atoms) and that each element has a different atom.
Thomson’s rules indicate that atoms have electrons that may be ejected.
Bohr’s rules indicate that electrons exist only in certain allowed energy levels in an atom.
How many electrons could the eighth shell in an atom contain?
2n^2: 2 x 8^2 = 2 x 64 = 128
How did Mendeleev organize his periodic table?
Mendeleev listed the elements vertically, in order of atomic mass (atomic weight). When he came across an element with properties similar to one higher on the list, he started a new column and placed the new element beside the one with similar properties.
State the periodic law and explain its meaning.
When elements are arranged by atomic number, their chemical and physical properties recur periodically. Many elements have similar properties and these properties follow a pattern that repeats itself regularly.
Compare and contrast groups and periods.
Each column in the periodic table constitules a group. Groups contain elements with similar chemical and physical properties. Each row in the periodic table constitutes a period. The atomic number of the elements increases sequentially across a period. the outermost electron shell that is occupied is the same for each element in a period.
Explain why each period ends with a noble gas.
A specific electron shell is filled as you go across a period. When the shell is filled, the period ends. Elements with filled out electron shells are noble gases.
Describe the basis for the different categories of the elements in the periodic table.
The elements in the periodic table are categorized in several different ways, In one case, elements are categorized by very spcufuc chemical and physical properties. Elements are also categorized by dividing the periodic table into blocks.
How do chemists define the radius of an atom?
The radius of an atom is the radius of a sphere within which electrons spend 90% of the time.
Why is it not possible to measure the size of an atom directly?
Electrons exist in a region that is best described as a cloud so atoms do not have defined boundaries. There is no way to directly measure the radius within which electrons spend 90% of their time.
How does the amount of charge in the nucleus of an atom affect the size of the atom?
As the charge of the nucleus increases, it exerts a greater force on the electrons. Thus, electrons in a given energy level, the electrons are drawn closer to the nucleus. As a result, the size of an atom decreases across a period from left to right in the periodic table
Explain the sheilding effect of electrons, and describe how it affects the size of an atom.
Increasing atomic order: oxygen (8), potassium (19), kryptin (36), tin (50) Increasing size (atomic radius): oxygen (73 pm), krypton (112 pm), tin (140 pm), potassium (227 pm) As the atomic number increases going across a period from left to right, the nuclear charge increases, which means there is more pull on the electrons and therefore the atomic radius decreases. Thusm within a period the progression of the atomic number and size are opposite. Going down a group, however, even though the atomic number increases, the effective nuclear charge is reduced due to shielding; the atomic radius therefore increases. Also, the number of occupied electron shells increases, making the atoms larger.
