atomic structure & periodic table Flashcards
what was john dalton’s theory on atoms
all matter is made from atoms
they cannot be created or destroyed
they are tiny, hard spheres
the atoms of an element are identical
what did cathode rays show
that when a high voltage is applied to a glass tube has most of the air removed, glowing rays are seen
JJ Thomson weighed the particles in the cathode rays and they were much lighter than the lightest atom, meaning that they were subatomic particles called electrons
what is the relative mass of a
proton
electron
neutron
p = 1 e = negligible (almost zero) n = 1
what is the relative charge of a
proton
electron
neutron
p = +1 (positive) e = -1 (negative) n = 0 (no charge)
what is in the nucleus of an atom
protons and neutrons
why do atoms have no overall charge
because they always have equal numbers of protons and electrons, so their positive and negative charges cancel each other out
why is most of the mass of the atom in nucleus
because the rest of the atom is empty space and electrons which weigh a negligible weight
how does the modern periodic table order the elements
by atomic number (number of protons)
what does the number in the top corner of the element represent
mass number (protons + neutrons)
what does the number in the bottom corner of the element represent
atomic number (protons only)
who discovered the neutron
james chadwick
why do isotopes explain how atoms of the same element can have different masses
because they have different amounts of neutrons which affect the weight
how did the understanding of neutrons lead to the discovery of nuclear energy
by firing neutrons at a uranium isotope, the nucleus could be split (nuclear fission) creating new elements and nuclear energy
what is the RAM of an element
the relative atomic mass is the mean mass of an atom compared with carbon-12, it takes into account isotopes and the amounts of each isotope. this means that RAMs are usually not whole numbers
how did mendeleev organise his periodic table
in order of increasing relative atomic masses but leaving some gaps for undiscovered elements and sometimes swapped some elements if it better suited their chemical properties
how are columns (groups) on the periodic table organised
similar chemical properties
how are rows (periods) on the periodic table organised
order of increasing atomic number
What did Henry Moseley discover
that the atomic number was equal to the number of protons in the atom’s nucleus, this was discovered by firing high energy electrons at different elements making them give off X-rays
where are the non-metals on the periodic table
on the right of the table
what is electronic configuration
the way in which an atom’s electrons are arranged
in the first 20 elements, what is the maximum amount of electrons the first three electron shells
2.8.8
how do you figure out electronic configuration
from the atomic number (number of protons = number of electrons)
how is electronic configuration related to the periodic table
- the number of occupied shells is equal to the period number
- the number of electrons in the outermost shell is the group number (group 0 elements have a full outermost shell)
what is a common chemical property for group 0 elements
being unreactive
