Science 9 - Chapter 2 Test Flashcards
Isotopic Forms
Atoms or elements may have several isotopic forms. For example, neon has two common forms, one with 10 neutrons and one with 12 neutrons.
Isotopes
Atoms that have the same number of protons but have different numbers of neutrons. Because they have the same number of protons they are the same element. Different numbers of neutrons make these different forms of the same element or atom.
How to distinguish two different isotopic forms?
To distinguish the two, they are described by their mass numbers. The form with 10 neutrons is described as neon-20. The form with 12 neutrons is described as neon-22. They can also be described in symbol form.
Where do electrons exist?
Outside the nucleus , but they have certain levels that they occupy. We call these levels Bohr electron shells, and they are part of a theory called the Bohr Atom. We will only deal with the first 20 atoms (first three Bohr shells) because atoms beyond these require another theory.
Maximum number of electrons
Each Bohr shell has a maximum number of electrons
1st shell maximum 2 electrons
2nd shell maximum 8 electrons
3rd shell maximum 8 electrons
When are atoms stable?
When they have a filled outer shell. When the valence shell is full the element does not want to gain or lose any electrons and is unreactive. When an element has one less than a full valence shell, it will pull the single excess electron from another element’s valence shell. This results in two stable atoms.
Ion || Charge
When an element has one more electron than proton (remember that protons are positively charged and electrons are negatively charged.) This gives it a net charge of -1. This stable species is now called a ion and is written differently.
Why is the Periodic table called the Periodic table?
Periodic means to recur regularly. In the periodic table there are certain characteristics that are periodic that is, regularly recurring.
Who created the periodic table? When?
Dmitri Mendeleev in 1867
5 things periodic table gives for each element
- atomic number
- symbol
- name
- atomic mass
- ion charge(s)
Ion’s Charge
An electrical charge that forms on an atom when it gains or loses electrons.
Ion
electrically charged atom
What properties do metals have?
- solid - except mercury (a liquid)
- shiny lustre
- good conductors of heat and electricity
- malleable
- ductility
What properties do non-metals have?
- some gases
- some solids
- only bromine is a liquid
- not very shiny
- poor conductors of heat and electricity
- brittle
- not ductile
What properties do metalloids have?
- solids
- can be shiny or dull
- may conduct electricity
- poor conductors of heat
- brittle
- not ductile
Which side of the staircase are metals found?
left side
what are the horizontal rows on the periodic tables called?
periods
What do the vertical columns on the periodic table called?
chemical families
what do the vertical columns have in common?
similar physical and chemical properties
4 well known families
alkali metals
alkaline earth metals
halogens
noble gases
Which alkali metal is most reactive?
cesium
what 2 substances do alkali metals highly react with?
oxygen and water
What ion charge do the alkali metals have
+
are alkali earth metals more or less reactive than alkali metals?
less
what ion charge do earth metals have?
+22
what family are fluorine, chlorine, bromine, and iodine a part of?
halogens
what ion charge do halogens have?
-
which halogens are gases?
fluorine and chlorine
which halogen is least reactive?
iodine
what ion charge do noble gases have?
0
will any of the noble gases react under normal conditions?
no
what are the properties of noble gas at room temperature?
colourless, odourless, gases
numbers of particles in an atom
Protons = atomic number
electrons = atomic number (in a neutral atom)
atomic mass = average mass of an element
mass number = protons + neutron*
neutrons = mass number - atomic number
*If you are not told anything else you could make a reasonable guess at a mass number by taking the atomic mass and rounding it to the nearest whole number
the nucleus
- is tiny
- is positively charged (all protons are in the nucleus)
- has most of the mass of an atom (protons & neutrons)
- protons and neutrons cannot be easily removed
electrons
- exist in shells outside the nucleus
- electron shell is negatively charged (contains only electrons)
- occupies most of the volume of an atom
- same number as protons if the atom is neutral (could differ if atom is charged)
what makes an ion charged?
number of electrons it gains or loses
rutherford’s model
Ernest Rutherford’s gold foil experiment led him to propose a nuclear atom, where there was a heavy nucleus in the center, with the electrons occupying the outer areas of the atom.
