Topic 2: Atomic Structure Flashcards
what is an element?
a substance that cannot be broken down into simpler substances by a chemical reaction
Daltons Model of an Atom
- all matter is composed of atoms
- atoms cannot be created or destroyed
- atoms of the same element are alike
- atoms of different elements are different
- atoms combine to form molecules
what is a compound?
a substance made by chemically combining two or more elements. It has different properties than its constituent elements
Rutherford’s model of an Atom
- fired alpha particles at a piece of gold foil; some bounced back
= atoms are mainly empty space and contain a positive nucleus
Proton
+1, in nucleus
Electron
-1, outside of nucleus (space outside)
Neutron
0, in nucleus
Mass Number (Ar)
number of protons plus number of neutrons in an atom
Isotopes
atoms of the same element with different mass numbers due to number of neutrons it contains (same electrons and protons however)
Relative average mass formula
total mass/number of atoms
positive ion
when an element loses an electron (cation)
negative ion
when an element gains an electron
anion
Relative Atomic Mass
weight mean of all naturally occuring isotopes of an element relative to carbon-12
decreasing wave frequencies/energy
Y-Rays X-Rays UV Radiation Visible light R Radiation Microwaves Radio waves
Continious spectrum
contains radiation of all wavelengths within a given range
e.g. visible light
Line spectrum
discrete lines of different wavelengths and frequencies
e.g. emmision or absorbtion spectra
Explain emmision spectrum of hydrogen atom
• The emission spectrum of hydrogen atom consists of different series of lines in different regions of the
electromagnetic spectrum.
• The lines in an emission spectrum are produced by excited electrons falling from higher to lower energy
levels: ΔEatom = hν = hc/λ.
• As the energy levels of the hydrogen atom converge at higher energy as they are further from the nucleus,
the lines in the spectrum also converge at higher energy/frequency.
- 2–>1 is the UV series
- anything to 2 is the visible light series (palmer)
Formula/relation between frequency and wavelength
• Frequency (ν) and wavelength (λ) are related by: c (speed of light) = ν λ.
• The energy of a photon (Ephoton) is related to the frequency (ν) of the radiation by Planck’s equation:
Ephoton = hν (the equation is given in section 1 of the IB data booklet)
h is Planck’s constant (see section 2 of the IB data booklet)
frequency
the number of waves that pass a certain point
IR Radiation
- long wavelength; short frequency; low energy
UV radiation
- short wavelength, high frequency, high energy
how is a line spectrum produced
when white light is passed through hydrogen gas
how is an emmision spectra produced
by providing hydrogen gas with high voltage
first ionization energy
minimum energy needed to remove one mole of electrons from one mole of gaseous atoms in their ground state
main energy levels of an atom and their energies?
- higher energy states= exicted electrons
- falling to ground state from high energy level has high energy
N= 1 (ground state)
N=2
N=3
N= infinity
how are lines the emission spectra produced
The lines in an emission spectrum are produced by excited electrons falling from higher to lower energy
levels: ΔEatom = hν = hc/λ.
Heisenbergs Uncertainty principle
- We cannot know where an electron of an atom is at a given time, so we use ‘probable diagrams’
Shrodigers model of the hydrogen atom
- atomic orbitals
- wave equation describes properties/behaviour of an electron
atomic orbital
- region around nucleus where there is a 90% probably of finding an electron
- different levels
- higher energy; more likely to find an electron further way from nucleus
Orbitals
Orbitals are regions in space in which an electron
may be found in an atom. Each orbital can hold two
electrons of opposite spin.
orbital shapes
s orbitals are spherical and p orbitals are dumb-bell shaped. There are three p orbitals orientated along the x, y and z axis.
Pauli exclusion principle
states that only electrons with opposite spin can occupy the same orbital.
Orbital diagrams
- used to describe the number of electrons in each orbital.
- Each orbital is represented by a box and each electron by a single-headed arrow which represents the direction of its spin.
energy levels
Each main energy level can hold a maximum of 2n^2
electrons.
• Each main energy level contains n sub-levels and n2
orbitals.
Aufbau principle
states that orbitals with lower energy are filled before
those with higher energy.
aufbau order
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4f, 5d, 6p, 7s …
