The periodic table Flashcards
How did Newlands order the periodic table?
Put known 62 elements in 7 groups according to their atomic weights
What is the law of octaves?
similar properties repeated every eighth element
Why were Newlands ideas not accepted?
After calcium their properties did not match well within the groups
What did Mendeleev do with the periodic table?
left gaps for undiscovered elements so that groups of known elements had similar properties
predicted properties of missing elements
Why were Mendeleev’s idea accepted?
His predictions were confirmed an his creation became the basis for modern periodic table
Why is it called the periodic table?
similar properties occur at regular intervals
What was discovered in the early 20th century and how did this affect the periodic table?
electrons, protons and neutrons were discovered so table arranged in order of atomic number. All the elements were placed in appropriate groups
What affects the reactivity in groups?
more occupied energy levels going down group so atoms get larger.
larger the atom, less strongly the outer electrons are attracted by nucleus.
What happens to reactivity going down the group in metal and why?
increases because they lose electrons when they react
What happens to reactivity going down the group in non-metal and why?
decreases because gains electrons when they react
What is group 1?
the alkali metals
Give three physical features of group 1 metals
soft solids
low melting and boiling points which decrease going down the group
low density - first three elements less dense than water ( float)
What happens when alkali metals react with water?
for hydrogen gas and metal hydroxide that is an alkali
what happens when group 1 elements react with non-metals?
form ionic compounds in which metal ion has charge on +1
What are the ionic compounds formed when alkali metals and non-metals react?
white solids that dissolve in water to form colourless solutions
What happens to reactivity going down group 1 as why?
increases because outer electron less strongly attracted to nucleus as atoms get larger so electron easier to lose
What are between groups 2 and 3?
transition metals/elements
Give features of transition metals
Not very reactive
High density and strong - used as building materials
Form positive ions with different charges
form coloured compounds
good catalysts
Malleable and ductile
good conductors of heat and electricity
What is group 7?
the halogens
Give features of group 7
non-metals
low melting and boiling points - i cease going down group
What happens when halogens reacts with metals?
form ionic compounds in which halide ion has charge of -1
How do they bond with other non-metals?
covalently to form molecules
What does a more reactive halogen do?
displaces a less reactive halogen from an aqueous solution of its salt
how does reactivity change going down group 7 and why?
decreases because outer electrons less strongly attracted to nucleus as atoms get larger. Electron less easily gained
