Flashcards in Elements, Atomic Structure, Radioactivity, Electronic Structure of Atoms Deck (156):
What do atoms consist of?
Three sub atomic particles and a dense nucleus
What are the three subatomic particles found in an atom?
Electron, neutron, proton
What is the relative charge of -
What is the relative mass [amu] of-
What is the location within an atom of
E- In energy levels orbiting the nucleus
Who discovered proton?
Who discovered neutron?
Who discovered the electron?
What do electrons occupy in an atom?
Definite energy levels orbiting the nucleus
Who discovered the existence of energy levels?
How did Niels Bohr find the existence of energy levels
He studied the emission spectra of hydrogen atoms that had been given energy and found a series of lines of specific energy, indicating that only specific energy jumps [absorbance and emissions] were possible in an atom
What provides strong evidence for the existence of energy levels within the atom?
What is the name given to the spectra of Paschen, Balmer, Lyman?
What region of the electromagnetic spectrum does Paschen lie?
What region of the electromagnetic spectrum does Balmer lie?
What region of the electromagnetic spectrum does Lyman lie?
What is an energy level?
It’s the fixed amount of energy that an electron can have in an atom
Where do energy levels start in atom?
Closest to Nucleus
What formula did Neil’s Bohr produce to work out the maximum number of electrons that would fit each orbital?
What are energy levels further divided into
What are sublevels?
Group of atomic orbitals, all of which have the same energy
What is an orbital?
A region in space where there is a high probability of finding electrons
What shape is an s orbital?
What shape is the P orbital?
Features of electrons
-occupy lowest available energy level
-fit max of two electrons in each sublevel
-not possible to determine the position and velocity of an electron at the same time
What causes the nuclear charge in an atom?
What is the atomic number?
It’s the number of protons in the nucleus of an atom
What does the atomic number tell you?
-position on periodic table
-number of electrons present
-number of protons
What is a mass number?
The sum of the number of protons and neutrons in the nucleus of an atom
What are isotopes?
Atoms of an element that contain the same number of protons but different number of neutrons and thus have different atomic masses
What is the relative atomic mass?
It’s the average mass of an atom of an element relative to one twelfth the mass of an atom of carbon-12
Why do we need a relative atomic mass?
In order to represent different varieties of isotopes and relative abundance’s
What is radioactivity?
It’s the spontaneous breaking up of unstable nuclei accompanied by the emission of radiation
What are the three different types of radiation?
Alpha particle, Beta particle, Gamma Ray
What is an alpha particle?
Helium nuclei with a positive charge and little penetrating ability
What is a beta particle?
Electrons with a negative charge and greater penetrating ability than alpha particles
What are gamma rays?
High energy electromagnetic radiation, with greater penetrating ability than beta particles
What stops penetrating power of an alpha particle?
A sheet of paper
What stops penetrating power of a beta particle?
5mm of aluminium
What stops penetrating power of an alpha particle?
Thick block of lead
Example of alpha particle and use
Example of beta particle and use
Carbon dating [archaeology]
Example of gamma ray and use
What is the reason for the difference in mass numbers of isotopes?
Different number of neutrons
What did the ancient greeks propose?
All substances are composed of four elements - earth, air, water and fire
What did Robert Boyle propose?
-an element is a substance that cannot be broken down into simpler substances by chemical means
What did John Dalton propose about the atom?
-atoms are tiny, indivisible, indestructible particles
-that are unique to each element
What did John Dalton propose about the element?
Elements combine to form compounds, they do so in fixed whole number ratios
What is the law of conservation of mass?
It states that matter is neither created nor destroyed in the course of a chemical reaction
What did Crookes discover?
Maltese cross placed in path of rays, cast sharp shadow at end of discharge tube
What did Johnstone Stony propose?
Suggested a name for the negative particles [cathode rays] - electrons
How did JJ Thomson discover electron?
Showed cathode rays were negatively charged particles when attracted to positive plate in electric field
What did Thomson discover
Their charge to mass ratio
What did Henry Mosley discover?
How did Henry Mosley discover the atomic number?
Using X-rays, measured the number of positive charges [later called protons] in atoms and found the number was different for every element - unique
What was the significance of the discovery of the atomic number?
Confirmed Mendeleev’s positioning of some elements in periodic table
What did Millikan discover?
Measured change of electron accurately, conducting his oil drop experiment
What did Rutherford discover?
Nucleus and Proton
How did Rutherford discover the nucleus?
Bombarded gold foil with alpha particles
What was the result of the Geiger-marsden experiment?
-few were repelled back
-most pass straight through
-some were deflected at large angles
What was concluded from Geiger marsden experiment?
Atom consists mostly of space, with a dense positive nucleus
How was the proton discovered?
Rutherford bombarded atom’s nuclei and eventually pushed out positive particles known as protons
What did James Chadwick discover?
How was the Neutron discovered?
Bombarded beryllium with alpha particles which caused neutral particles with same mass as protons to be pushed out
What did Niels Bohr discover?
The existence of energy levels, that electrons have fixed energies
Defined energy levels and 2n^2
What does the Heisenberg uncertainty principle state?
It is impossible to measure the velocity and position of an electron at the same time
What did Humphrey Davy discover?
Isolated new elements such as calcium and magnesium using electrochemical techniques
What did Dobereiner propose?
Law of triad -
Chemicals with similar properties were to be grouped in threes, the middle one having a mass midway between the other two
Discovered, Li, Na, K
What did Newlands propose?
Law of octaves
Chemical properties of every eight element were repeated
What did Mendeleev propose?
Arranged elements known and unknown in periodic lines according to increasing atomic weight
What did Becquerel discover?
Spontaneous radioactive emissions
What did Marie Curie discover?
Isolated two highly radioactive elements -polonium and radium
Who coined the term “radioactivity”
What substance was used to discover polonium and radium?
What substance was used to discover spontaneous radioactive emissions?
What were the features of elements in a triad?
-similar chemical properties
-atomic weight of the middle elements would be midway between the other two
What was the law of triads limitation?
Restricted to only a small number of elements
What link made by dobereiner was essentially important in drawing up periodic table?
Link between different elements depended upon atomic weights
Limitations of the law of octaves
-tried to force all known elements to fit pattern and fitted very reactive metals in the same group as unreactive metals
-only worked for a small number of elements
What relationship was made in the periodic table?
Properties of elements and their atomic weights
Differences between Mendeleev’s periodic table and the Modern Periodic table
gaps left for undiscovered elements
in order of increasing atomic weight
in order of increasing atomic number
What property of cathode rays allowed Thomson to measure charge to mass ratio
They are deflected by magnetic fields
Describe Thompson’s plum pudding model
Atoms were positive spheres in which negatively charged electrons were embedded
Who disproved plum pudding model?
instead - mostly made up of empty space with positive dense nucleus, electrons orbiting nucleus
What was the Bohr Model of the Atom?
Electrons were arranged in a series of concentric circular orbits at an increasing distance from the nucleus
Name the series of coloured lines in the line emission spectrum of hydrogen corresponding to transitions of electrons from higher energy levels to the second n=2 energy level
Name the series of coloured lines in the line emission spectrum of hydrogen corresponding to transitions of electrons from n=3 to n=1
Give an example of a radioactive isotope and state one common use made of this isotope?
Americium -241 [smoke alarms]
Carbon -14 [archaeological dating]
What is used to calculate the relative atomic mass of an element?
What is the principle of the mass spectrometer?
Positive charged ions are separated on the basis of their relative masses moving in a magnetic field
What are the five processes in mass spectrometry?
Give a use of mass spectrometry
Explain what occurs in vaporisation in mass spectrometry
Sample becomes heated and turns into a gas
Explain what occurs in ionisation in mass spectrometry
High energy electrons are shot at sample which knocks out an electron to form a positive ion
Explain what occurs in acceleration in mass spectrometry
Passes through an electric field to accelerate positive ions to high speed
Explain what occurs in separation in mass spectrometry
Pass through magnetic field and are deflected : lighter ions are deflected more than heavier ions. in this way, particles with different masses can be separates and identified
Explain what occurs in detection in mass spectrometry
ions are detected
What instrument was fundamental in detecting the existence of isotopes?
What is the difference between a nuclear reaction and a chemical reaction?
Chemical - changes in distribution of electrons, cannot change one element into another element
Nuclear - changes in nucleus and can cause elements to change into other elements
What is a radioisotope?
Unstable, radioactive isotopes
What is the half-life of a radioactive isotope?
It’s the time taken for half of the atoms in a sample of the isotope to decay
What gas makes up more than half of the background radiation?
What are we told from carrying out the flame test
Each metal has their own characteristic colour, therefore the colours obtained can be used to identify the metals present in unknown compounds
Why is the line spectrum of each element unique?
The spacing between energy levels in terms of energy are also unique in atoms of that element
What colour does barium turn in flame tests?
What colour does copper turn in flame tests?
What colour does lithium turn in flame tests?
What colour does potassium turn in flame tests?
What colour does sodium turn in flame tests?
What colour does strontium turn in flame tests?
Procedure for flame tests
-using a soak wooden splint
-crush a little bit of the salt to be tested using mortar and pestle
-dip wooden splint in salt and put over Bunsen flame and note the characteristic colour given off
-repeat the experiment with other salts
Why is the emission spectra useful in identifying an element?
The emission spectrum of an element is characteristic of that element
What is the ground state?
The lowest energy state
What is the excited state?
A higher energy state
What occurs when energy is emitted in an atom?
Electron moves from a higher energy level to a lower energy level
Under normal circumstances, where is the hydrogen electron found?
The ground stage
What occurs if an electron receives enough energy?
It will move to an excited state [here it’s relatively unstable]
Why does the electron in the hydrogen often atom eventually fall back down?
It is unstable in the excited state, therefore drops back down emitting energy
What is the aufbau principle?
States that electrons will occupy the lowest energy sublevel available
What is the atomic radius of an element?
It is half the distance between the nuclei of two atoms of the element that are joined together by a single covalent bond
Describe and account for the trend in atomic radii of the elements across the second period
Increase in Nuclear charge - exerts a greater attractive force on the outer electrons
No screening effect - electrons are held closer and therefore radius is smaller
Describe and account for the trend in atomic radii of the elements going down a group
Addition of extra energy levels -increase in number of filled shells
Screening effect - electrons in inner shells partially neutralise the nuclear charge by repelling the outer electron
What is first ionisation energy
It’s the energy required to remove the most loosely bound electron from an isolated atom in its ground state
What is the equation of first ionisation energy?
X -> X^+ + e^-
What is the first ionisation energy measured in?
KJ per mole
Describe and account for the trend in first ionisation energy of the elements across period
General increase -
Increase in nuclear charge which holds the electrons more tightly making them difficult to remove
Decrease in atomic radius holds electrons in more tightly and also make them difficult to remove
No screening effect
Describe and account for the trend in first ionisation energy of the elements going down a group
Increase in atomic radius makes it easier to remove an electron despite the increased nuclear charge
Screening effect of inner levels - electrons in inner shells partially neutralise the nuclear charge by repelling the outer electron
Account for the decrease in first ionisation energy between nitrogen and oxygen
[write out electronic configuration]
Nitrogen is more stable due to its half filled 3p orbital
Oxygen has a pair of electrons in px sublevel. If electron was taken away it would be stable.
Explain why the second ionisation energy of sodium is significantly higher than the first while the increase in the second ionisation energy or Neon compared to its first is relatively small
[write out electronic configuration]
Na = 1st electron removed is from the third shell which gives sodium a high stability configuration, but loss of second is from high stability atom, higher
Ne = both electrons are removed from same sublevel
Peaks in trend table
High peaks, low peaks and medium peaks
[draw electronic configuration]
The high peaks - represent already stable atoms with filled p sublevel
Medium peaks - half filled sub levels or filled sublevels
Low troughs - atoms happy to have electrons removed due to unstable electronic configuration
HIGH = STABLE
LOW = UNSTABLE
What is the second ionisation energy?
Minimum energy required to remove the most loosely bound electron from each monopositive ion in a mole of these ions
How is the second ionisation energy represented in an equation?
X^+ -> X2+ + e^-
How does the definition of second ionisation energy differ from that of first ionisation energy?
The electron is removed from each monopositive ion
Evidence supporting Bohr Theory
-ionisation energy always rises due to protons in the nucleus pulling on less and less electrons causing a decrease in the radius of an atom
-energy jumps = small differences between ionisation energies for electrons belonging to the same shell but large differences of electrons are removed from different shells
-only worked for hydrogen
-did not take into account of wave-particle duality
-did not take into account Heisenberg’s uncertainty principle
-didn’t include the discovery of sublevels
Features of transition metals
High boiling /meltingpoints
Calculate the mass of sodium chloride required to prepare 500cm^3 of a .9% w/v saline solution
450/100 - 4-5 g
M^2+ has 25 electrons and 32 neutrons
What is the atomic number and the mass number?
Atomic number [protons] - 27
Mass number [protons and neutrons] - 59
How many electrons and neutrons has the aluminium ion
13 Al ^3+
Electrons [-3] - 13-3 = 10
Neutrons - 27-13 = 14
Explain why relative atomic masses are rarely whole numbers
Average of mass numbers of isotopes of an element
What changes take place in the nucleus of an atom when beta decay occurs?
Neutron changes into proton
When 19.05g of copper reacted with nitrogen, 20.45g of copper nitride.
Deduce the empirical formula of copper nitride
19.05/64 - .3
20.45-19.05 = 1.4/78 = .1
Find the empirical formula of a compound containing 40% sulfur and 60% oxygen, by mass
40/32 - 1.25
60/16 - 3.75
Calculate the daly mass of potassium iodide needed to supply .15mg of iodide ion
.15/127 - .00118
.00118 x 166 - .196
How many neutrons are there in
.14g of carbon 14
.14/14 - .01
.01 x 6 x 10^23 x 8 NEUTRONS =
When hydrogen gas was passed over 1.59g of copper oxide, 1.27g of metallic copper were produced. Find by calculation the empirical formula of the copper oxide
1.59 - 1.27 = .32
1.27/64 = .02
.32/16 = .02
Complete and balance the equation for the chemical reaction that occurs when sodium is added to ethanol
C2H5OH + Na ->
C2H5OH + Na -> C2H5ONa + 1/2 H2
State the number of sublevels and orbitals in an argon atom (atomic no : 18)
Sublevels - 5 (s,s,p,s,p)
Orbitals - 9 (s,s,px,py,pz,s,px,py,pz)
Write a balanced nuclear equation for the beta particle decay of iodine-131 (atomic no - 53)
131 I -> 0 é + Xe
Give two properties of cathode rays
Travel in straight lines
Write the electron configuration of the oxygen (oxide) ion O2-
How many atoms of iron are there in a 30g bowl of cornflakes that contains .0024g of iron per 30g serving
.0024/mr(56) = 4.29 x 10-5 x 6 x 10^23 = 2.6 x 10^19
How many iron atoms should be consumed daily to meet the recommended daily intake of iron in a diet of 0.014g
.014 / 56 = .00025 x 6 x10^23 = 1.5 x 10^20
A 500cm^3 can of beer contains 21.5cm^3 of ethanol. Calculate its % alcohol
21.5/500 x 100/1 = 4.3%
Name the scientist who identified cathode rays as subatomic particles