4. The Periodic Table Flashcards
What did the Greeks believe about elements?
4 elements: earth, fire, air , water
EFAW
What scientist in 1661 gave a simple definition of an element?
Robert Boyle, from Waterford
Element
An element is a substance that cannot be split into simpler substances by chemical means
Which scientist in 1829 put elements with similar properties in triads?
Dobereiner
Triad and the problem with this theory
A triad is a 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.
Eg Lithium Sodium Potassium (group1)
Prob: few other triads found
Who was the first scientist to arrange elements in order of increasing atomic weight in 1864?
Newlands
Newland’s octaves
Newland’s octaves are arrangements of elements in which the first and the eighth element, counting from a particular element, have similar properties.
Mendeleev’s Periodic Law
When elements are arranged in order of increasing atomic weight, the properties of elements recur periodically
I.e the properties displayed by an element are repeated at regular intervals by other elements
What 3 things did Mendeleev do?
- He left gaps for undiscovered elements and correctly predicted their properties
- He switched some pairs of elements around to make sure they would fit in with the properties expected of that group
- Transition metals did not have a separate block
Which scientist arranged elements in order of increasing atomic number in 1913?
Moseley
Atomic number
Atomic number of an atom is the number of protons in the nucleus of the atom
Modern Periodic Law
When elements are arranged in order of increasing atomic number, the properties of elements recur periodically
I.e the properties displayed by an element are repeated at regular intervals by other elements
What are 2 features singular to Moseley’s periodic table?
- No gaps
- Transition metals have a separate block
Mass number
The mass number of an element is the sum of the number of protons and neutrons in an atom of that element.
How to calculate no. of neutrons
Neutrons : Mass no. - Atomic no.
What is the chemical symbol for mass no.?
A
What is the chemical symbol for atomic no.?
Z
Isotopes
Isotopes are atoms of the same element (they have the same atomic no.) which have different mass no. due to the different no. of neutrons in the nucleus
Relative atomic mass
- the average of the mass no’s of the isotopes of an element,
- as they occur naturally,
- taking their abundances into account
- and expressed on a scale relative to 1/12th the mass of 12C.
Principle of mass spectrometry
The principle of mass spectrometry is that charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses.
What are the 5 stages of mass spectrometry?
- Vaporisation
- Ionization
- Acceleration
- Separation in the magnetic field (analyser)
- Detection
Vaporisation
Liquid sample is turned to gas in the vacuum
Ionization
High energy electrons are fired from an electron gun to knock out electrons from atoms of the sample, leaving cations in their place
Acceleration
Cations pass through a series of negatively charged plates. These plates attract the pos.ions, thus accelerating them into the analyser unit as a fine beam.
Separation in the magnetic field
an electromagnet is used to deflect ions. Lighter ions are easier to deflect, heavier ions harder. Thus ions are separated into separate beams according to their masses.
Detection
Ions fall on detector. Detector amplifies signal into sizeable electric current which can be viewed on a computer screen. By changing strength of magnetic field, ions of different masses fall on detector, producing a mass spectrum.
Uses of mass spectrometer , social use
-identify presence of isotopes
-identify unknown compounds
-measure relative abundance of isotopes + relative atomic mass
——— test for drugs , athletes, Garda
Electron configuration
The electron configuration shows the arrangement of electrons in an atom of an element .
Aufbau principle
When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy levels.
Which two elements are special in their electronic configurations ? How? And why?
Copper (Cu): 4s1, 3d10
Chromium (Cr): 4s1, 3d5
Sub levels that are half filled or completely filled have extra stability, so an electron from the 4s “flips” over
Hund’ s rule of Maximum Multiplicity
When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.
Pauli Exclusion Principle
states that .. no more than two electrons can occupy an orbital and they must have opposite spin.
What are the names of the orbitals in the p sublevel?
Px, py, pz
