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CHEM CHAPTER 3: Electrons and the Periodic Table (3.3: TRENDS IN THE…
CHEM CHAPTER 3: Electrons and the Periodic Table
3.1: ELECTRONIC STRUCTURE OF ATOMS
3.2: ELECTRON ARRANGEMENT IN PERIODIC TABLE
3.3: TRENDS IN THE PERIODIC TABLE
LEFT TO RIGHT
core charge increases
radius decreases
electronegativity increases
first ionising energy increases
TOP TO BOTTOM
radius increase
first ionising energy decrease
electronegativity decrease
first ionisation energy = the energy required to remove one electron from an atom of an element in the gas phase
the magnitude of this energy reflects how strongly the valence electron is attracted to the nucleus of the atom
electronegativity = the ability of an atom to attract electrons in a covalent bond towards itself
the more strongly the valence electrons of an atom are attracted to the nucleus of the atom, the greater the electronegativity
core charge
= measure of the attractive force felt by the valence electrons towards the nucleus
= number of protons in the nucleus - number of total inner-shell electrons
metallic character
IN GENERAL
atoms containing 1, 2 or 3 valence electrons tend to behave as metals
those with 4 or more valence electrons behave as non-metals
3.4: QUANTISATION OF ENERGY
electrons in atoms can only be found at discrete energy levels
these are the energies associated with the shells in which the electrons can be found. described as quantised (restricted to discrete values)
electrons can jump up or down between these levels by absorbing or emitting energy
when the electron is in the lowest state of energy (n = 1 shell) is is called ground state
when an atom is heated up, the electron can absorb the energy and jump to a higher level. this higher energy state is called the excited state
Electromagnetic radiation
= a kind of radiation including visible light, radio waves, gamma rays, and X-rays
electromagnetic spectrum = the range of different forms of electromagnetic radiation
radiation from each portion of the electromagnetic spectrum can be described in terms of its frequency, wavelength and energy
Absorption spectra
when a sample of a particular element's atoms are exposed to a spectrum of visible light, the sample will only absorb the certain colours which correspond to the specific energy levels of the atom's shells
the specific colours absorbed by the sample show up as lines on the electromagnetic spectrum called absorption lines. collectively, all the lines together for one element sample form an absorption spectrum
Emission spectra
heating an element up gives energy --> electron moves up energy level
cooling element down takes energy back away --> electron moves back down energy level and releases the energy difference
again, certain amounts of energy correspond to specific colours so when specific amounts of energy are emitted (shown through the particular colour that it matches up with) we can tell which energy levels an electron has moved from
these lines are shown as emission lines on an emission spectrum
3.5: SPECTROSCOPY
= the study of interactions between matter and electromagnetic radiation
is the basis for a number of qualitative and quantitative analytical techniques
Flame tests
some metals produce particular colours when they are heated
thus the metallic elements present in a compound can often be determined by placing a sample in a bunsen burner flame
LIMITATIONS:
Qualitative only
Only a small range of metals are detectable by the flame test
Metals in low concentration may be difficult to observe
Mixtures of metals will produce confusing results
Atomic Absorption Spectroscopy (AAS)
sample is vaporised in a flame to produce free atoms in their ground state. These atoms are then sent through the optical path of a light source, which produces an emission spectrum of the particular sample
BENEFITS:
Qualitative and Quantitative results
More than 70 elements can be analysed
Can detect elements in concentration as low as a microgram/L