chapter 12 - the periodic table Flashcards
- describe the periodic table
a method of classifying elements and its use to predict properties of elements.
how are elements arranged in the periodic table?
the are arranged according to their proton number.
thus, the elements show periodicity: elements with similar properties appear at regular intervals.
the similar elements are arranged into columns.
what are the columns numbered I to VIII?
Families called groups.
what are the rows numbered 0 to 7?
periods.
what is the point of the zig-zag line?
it separates metals from non-metals
metals to the left (except for hydrogen)
non-metals to the right
*describe and explain the relationship between
Group number, number of outer shell electrons
and metallic/non-metallic character
the group number is the same as the number of outer shell electrons in the atoms.
outer shell electrons dictate how an element behaves.
all elements in a group have similar reactions.
elements of group VIII elements have a very stable arrangement of e- —> unreactive.
groups I to III lose e- —> metals except for boron.
groups IV to VII gain e- —> non-metals.
metallic character of the elements increases as you go down a group
atoms with the same number of valency electrons react in a similar way.
what is another name for outer-shell electrons?
and what is valency?
valency electrons
valency is the number of electrons atoms of an element lose, gain or share, to form a compound.
what does the period of an element tell you?
the number of electron shells in the atoms.
what are artificial elements?
ex) neptunium (Np), lawrencium (Lr).
they have been created in a lab.
they are radioactive, their atoms break down very quickly, that is why they aren’t found in nature.
*describe the change from metallic to non-metallic character across a period
across a period there is a trend, a change from metal to non-metal.
what are alkali metals?
they are the elements of group I
what are the physical properties of alkali metals?
they are not typical metals:
- good conductors of heat and electricity
- softer than most metals, can be cut with a knife.
- shiny silvery surfaces when freshly cut.
- have low densities, float on water- while reacting with it.
- low melting and boiling points, compared with most metals.
from what you’ve learnt above
*Describe lithium, sodium and potassium
- they are elements of Group I
- a collection of relatively soft metals showing a trend in melting point, density and reaction with water.
*identify the trends in physical properties of group I
- softness increases going down the group
- density increases going down the group
- melting and boiling point decreases going down the group.
describe the reactivity of alkali metals
alkali metals are the most reactive of all the metals.
1- they react vigorously with water. hydrogen bubble off, leaving solutions of their hydroxides which are alkalis.
2- when they react with chlorine, they burst into flame, burn brightly, forming chlorides.
3- the burn fiercely in oxygen to form oxides, which can dissolve in water to give alkaline solutions.
explain why alkali metals are so reactive
- they need to lose only one e-, to gain a stable outer shell.
- they have a strong drive to react with other elements and compounds, in order to give up this 1 electron.
- form positive (1+) ions.
- they form ionic compounds.
- they are usually kept under oil to stop them from reacting.
explain why alkali metals react in similar ways
- lithium floats and fizzes.
- sodium shoots across the water.
- potassium melts with the heat of the reaction, and the hydrogen catches fire —> burns with a lilac flame.
they react in a similar way because they have the same number of valency electrons.
*identify the trends in chemical properties of group I
- reactivity increases going down the group
explain why reactivity of alkali metals increases going down the group
- As you go down Group 1, the number of shells of electrons increases by 1 (Period number increases down the Periodic table).
- This means that the outer electron is further away from the nucleus so there are weaker electrostatic forces of attraction.
- This requires less energy to overcome the electrostatic forces of attraction between the negatively charged electron and the positively charged nucleus.
- This allows the electron to be lost easily, making it more reactive as you go down the Group
what are the halogens?
- elements of group VII.
all halogens form colored gases, are poisonous, form diatomic molecules.
from what you’ve learnt above
*Describe the halogens, chlorine, bromine and
iodine
- elements of Group VII.
- a collection of diatomic non-metals showing a trend in color and density.
*identify the trends in physical properties of group VII
F2 --> yellow gas Cl2 --> green gas Br2 --> red liquid I2 --> black solid - color gets deeper going down the group - density increases going down the group - boiling point increases going down the group
*identify the trends in chemical properties of group VII
- reactivity decreases going down the group
why are halogen so reactive?
- their atoms need just one more e- to reach a stable outer shell.
- they have a strong drive to react with other elements or compounds, to gain this 1 e-.
- form negative (1-) ions.
