Key concepts.1 Flashcards
Describe how the dalton model of an atom has changed over time because of the discovery of subatomic particles
1803 Dalton
Solid atom model : all atoms of an element are identical; different elements have different atoms
1897 Thomson
Discovers the electron
1904 Thomson
Plum pudding model : atoms are spheres of positive charge with negative electrons dotted around inside
1911 Rutherford
Solar system model: atoms have a positive nucleus surrounded by negative electrons in orbits
1913 Bohr
Electrons shell model: electrons occupy shells or energy levels around the nucleus
1918 Rutherford
Proton discovery
1932 Chadwick
Neutron discovery
Structure of the atom
Nucleus containing protons and neutrons
Surrounded by electrons in shells
Relative charge and mass of a proton
Charge is +1
Mass is 1
Relative charge and mass of a neutron
Relative charge = 0
Relative mass = 1
Relative charge and mass of and electron
Relative charge = -1
Relative mass = 0.0005 or 1/1836
Why do atoms have equal numbers of protons and electrons
By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons.
Neutral overall
What’s the size of the nucleus compared to the atom
Very small
Where is most the mass in an atom
Concentrated in the nucleus
Define mass number of an atom
The mass number (symbol A, from the German word Atomgewichte (atomic weight), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.
If several atoms have the same number of protons what does this mean?
It’s the same element and this number is unique to this element
What’s an isotope
Different atoms of the same element containing the
Same no of protons
Different no of neutrons in their nuclei
Atomic number =
Number of protons
Mass number =
Protons + neutrons
How does the existence of isotopes result in relative atomic masses of some elements not being whole numbers
X
How would you calculate the relative atomic mass of an element from the relative masses and abundance’s of its isotopes
Multiply the mass number of each isotope by its relative abundance and then add them all together and divide by 100
Gallium has two isotopes gallium-69 and gallium-71
Relative abundance of gallium-69 is 60% calculate the relative atomic mass of gallium
Relative abundance of gallium-71
= 100%-60%=40%
Relative atomic mass = (69x60) + (71x40)/100
= 4140 + 2840/100
= 69.8
Describe how medeleev arranged the elements, known at that time in a periodic table using properties of these elements and their compounds
1869
Order of relative atomic masses
Checked properties of element and compounds
Swapped places of some so that elements with similar properties lined up
Left gaps where he thought there were other elements and predicted there properties
When these were discovered Mendeleev predictions fitted the properties very well
Mendeleev thought he had arranged elements in order of increasing atomic mass why was this not always true?
The positions of elements in some pairs were reversed
Because some of the relative abundance of istotopes of some pairs of elements in the periodic table
How are elements arranged in the periodic table now
In order of increasing atomic number
Rows are called
Periods
Vertical columns are called
Groups
Where are elements with similar properties placed
In same groups/vertical columns
Group 6 elements
Don’t react with water
All react with oxygen except oxygen
All from compound with hydrogen with the general formula: H2X
6 electrons in their atoms outer shell
Group 7 elements
All react with water
Don’t react with oxygen
All from compounds with hydrogen with the general formula : HX
7 electrons in their atoms outer shell
