Ch4: The Periodic Table Flashcards
What contributions did the Greeks make towards the periodic table?
They said that the universe was made up of 4 elements: earth, air, fire, water
What was the order of people that contributed towards the periodic table?
-Greeks
-Robert Boyle
-Humphry Davy
-Johann Dobereiner
-John Newlands
-Dmitri Mendeleev
-Henry Moseley
-Francis William Aston
What contributions did Robert Boyle make towards the periodic table?
He developed the definition of an element
Element: a substance that cannot be split up into simpler substances by chemical means
What contributions did Humphry Davy make towards the periodic table?
Discovered many elements by passing electricity through their compounds (electrolysis)
-Potassium, sodium, calcium, barium, strontium, magnesium
PSSCBM
What contributions did Johann Dobereiner make towards the periodic table?
Arranged triads
Triads: group of three elements with similar chemical properties, in which the atomic weight (relative atomic mass) of the middle element, is approximately equal to the average of the other two
Give examples of Dobereiner’s triads
-Chlorine, Bromine, Iodine (CBI)
-Calcium, Strontium, Barium (CSB)
-Lithium, Sodium, Potassium (LSP)
-Sulfur, Selenium, Tellurium (SST)
What contributions did John Newlands make towards the periodic table?
He arranged known elements in order of their atomic weights and created The Law of Octaves
Newland’s Octaves: arrangements of elements in which the first and the eight element, counting from a particular element, have similar properties
What were the problems with Newland’s Octaves?
-Oxygen and sulfur do not resemble iron in chemical properties (OSI_)
-Nitrogen and phosphorus do not resemble manganese in their properties (NPM)
-The noble gases were missing as they had not been discovered yet
-No gaps were left for elements that were yet to be discovered
-Only worked for the first 16 elements or so
What contributions did Dmitri Mendeleev make towards the periodic table?
He created Mendeleev’s Periodic Law
-When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements recur periodically
What were the differences between Newland’s and Mendeleev’s Periodic table?
-Mendeleev left gaps to make elements fit into the proper column
-He announced that these gaps were left for elements that had yet to be
-He was able to predict the properties of some elements that had not been discovered yet
What did Mendeleev do to fix some of the problems with his periodic table?
He had to reverse the order of some of the elements to make them fall into groups of elements with similar properties
e.g. Iodine originally came before Tellurium but he reversed them
-He normally arranged elements in order of atomic weight but realised that properties were more important than atomic weight
What contributions did Henry Moseley make towards the periodic table?
He created the modern periodic table
How did Moseley make the modern periodic table?
-He found a way of determining the number of protons in the nucleus of an atom, using x-rays, therefore finding the atomic number
-He showed that if elements in the Periodic table were arranged in order of atomic number, and not atomic weight, there is no need to swap some around
What is atomic number (Z)?
Number of protons in the nucleus of that atom
What is the modern periodic table?
An arrangement of elements in order of increasing atomic number
What is the modern periodic law?
When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically
What are the differences between Mendeleev’s periodic table and the modern periodic table?
-Modern: elements arranged in order of increasing atomic number
-Mendeleev: elements arranged in order of increasing atomic weight
-Modern: over 100 elements
-Mendeleev: approx. 60 elements
-Modern: no gaps
-Mendeleev: Gaps for undiscovered elements
-Modern: transition elements are in a separate block
-Mendeleev: transition elements were not in a separate block
What is the mass number (A)?
The sum of the number of protons and neutrons in the nucleus of an atom of that element
What does a.m.u. stand for?
Atomic Mass Unit
What are isotopes?
Atoms of the same element which have different mass numbers due to their different number of neutrons in the nucleus
What is relative atomic mass (Ar) and what was it previously called?
-Previously called the atomic weight
Defined as:
-The average of the mass numbers of the isotopes of an element
-As they occur naturally
-Taking their abundances into account
-Expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units
Who invented the mass spectrometer?
Francis William Aston
What are the uses of the mass spectrometer?
-To identify the presence of isotopes
-To measure relative abundances
-To measure the relative atomic mass of an element
What is the principle of mass spectrometry?
Charged particles moving in a magnetic field are deflected to different extents according to their masses, and thus separated by these masses
Name the processes of the mass spectrometer
- Vaporisation
- Ionisation
- Acceleration
- Separation/Deflection
- Detection
Explain vaporisation
-A small amount of gas or liquid is injected into the sample inlet
-If it is a liquid, it is vaporised using a vaccum
Explain ionisation
-Atoms or molecules are turned into ions using an electric gun
-These electrons are fired at the sample and knock out electrons from the sample particles to produce positive ions
Explain acceleration
-Positive ions pass between a series of negatively charged plates
-Because the positive ions are attracted to the negative plates, they are accelerated
-A fine beam of ions are passed into the analyser
Explain separation/deflection
-In the analyser, the particles move in a curved path and are deflected using a magnetic field
-The ions are separated according to their masses (Lighter particles are pushed further off course than heavier ones bc they are easier to deflect)
Explain detection
-By changing the strength of the magnetic field, the operator brings ions of different masses to the focus on the detector
-The signal is then amplified into an electric current and viewed on a computer screen
-It is then sent to a recorder
Why are vacuums needed inside a mass spectrometer?
-To vaporise liquids
-To allow particles to move along without colliding with any air molecules
What is electron configuration?
Shows the arrangement of electrons in an atom of an element
What is the Pauli Exclusion Principle?
States that no more than 2 electrons may occupy an orbital and they must have opposite spin
What is the Aufbau Principle?
When building up electron configurations of an atom in its ground state, the electrons occupy the lowest available energy levels
What is Hund’s Rule of multiplicity?
When 2 or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs
