The Periodic Table 1 Flashcards
elements
a substance that cannot be split into simpler substances by chemical means (robert boyle)
triads
a triad is a group of 3 elements with similar chemical properties in which the atomic weight of the middle element is aprox equal to the average of the other 2 (dobereiner)
octaves
arrangement of elements in which the first and eighth elements counting from a particular element have similar chemical properties. (newlands)
what did Humphry Davy do?
discovered elements by passing electricity through compounds and laid the ground work for more elements to be discovered by passing electronic currents through samples
limitations of octaves
some elements werent discovered yet (noble gases) and he should have left gaps
it only worked for the first 16 elements
limitations of triads
only a few were found
mendeleev’s periodic law/system
when elements are arranged in order of increasing atomic mass number
the properties of the elements repeat periodically in columns of similar chemical properties
moseley’s or modern periodic law
elements arranged in order of increasing atomic number
the properties of the elements repeat periodically
advantages of modern periodic law
no need to reverse the order of elements to make them fall into groups of similar properties
** elements automatically fall into the correct
groups**
no gaps
differences between mendelev and moseley
mendeleev:
increasing atomic mass no
only 60 elements dicovered
gaps appeared for undiscovered elements
modern
elements placed in order of increasing atomic number
more than 100 elements discovered
no gaps
why is the periodic table useful
- gives atomic and mass no of each element
- used to calculate the relative molecular mass of molecules
- writing electronic configuration and counting subatomic particles
isotopes
atoms of the same element that have the same atomic no due to the same amount of protons and electrons but they have a different mass number due to the different no of neutrons in the nucleus.
do isotopes react in the same way? why or why not?
chemical reactions are based on electrons. since different isotopes of the same element have the same no of electrons they react in the exact same way. neutrons do not effect it.
relative atomic mass
the average mass no of all the isotopes of an element as they occur naturally taking their abundances into account.
relative to 1/12th of the mass of a carbon -12 isotope.
why is the mass no on the periodic table never whole number?
all elements exist as a mixture of isotopes
the ram is the mean mass of all isotopes of one atom compared to the mass of 1/12th of the mass of a carbon 12 isotope.
it takes into account the amount and type of element of each isotope.
therefore the mass no is rarely a whole no as it is an average.
what is the RAM formula
(% isotope 1 x mass of isotope 1)+(%I2 x M2) divided by 100
what does it mean when a question says respectively when asking about the RAM formula?
that the percentages and masses go together in the order they are asked in the question
The principle of mass spectrometry
charged particles moving in a magnetic field are deflected and separated by different extents or amounts according to their masses
uses of a mass spectrometer
detect the presence of isotopes and identify unknown compounds.
measure the relative abundances, relative atomic mass and relative molecular mass of isotopes.
what are the 5 stages of the mass spectrometer in order
vaporisation
ionisation
acceleration
separation
detection
description of vaporisation
sample to be analysed is injected. the machine is kept under vacuum which converts liquids to gases
description of ionisation
electron gun fires electrons at the gaseous atoms, knocking electrons from the atoms. this forms (+) charged ions.
description of acceleration
(+) ions pass between (-) charged plates that attract and accelerate the (+) ions
description of separation
(+) ions are deflected in a magnetic field. lighter ions are deflected more, heavier ions less. ions are separated according to their masses
description of detection
(+) ions strike a detector. signal is amplified and a mass spectrum is produced
atomic number
the number of protons found in a nucleus. also shows the order of elements in the periodic table.
atomic mass number
the sum of number of protons and Number of neutrons in the nucleus.
why were there gaps in mendeleev’s periodic table
gaps appeared for undiscovered elements
why did mendelev reverse the order of some elements such as Te and I
to make them fall into groups with similar chemical properties
in what way did mendeleev arrange his periodic table
In order of increasing atomic mass no and elements were placed into groups of similar chemical properties
what else did medeleev do?
predicted to properties of undiscovered elements
how did mendeleev predict the properties of undiscovered elements
elements were placed into groups of similar chemical properties and by knowing the properties of the other elements elements in the same group he could predict how the unknown element will behave
explain why x ion has a charge of +/- y after it has lost z e-
write of the no of protons, electrons and neutrons in the ground state and the ion and then say therefore there are x more protons/e- in the ion so there are x more pos/neg charges.
by refering to subatomic particles, explain why x and y are considered isotopes
give definition
show how many protons, neutrons and e- are in each
