chemical patterns Flashcards
whats the equation for the reaction between sodium and chlorine?
sodium + chlorine —> sodium chloride
2Na + Cl2 —> 2NaCl
how does sodium react with chloride?
vigorously, to give a yellow flame
whats the equation for the reaction of group 1 elements with water?
metal + water —> metal hydroxide + hydrogen
what are group 1 metals?
flammable, hydroxides harmful and corrosive
should be kept away from water and naked flames
when working with halogens, what should you do?
- safety glasses
- avoid working near naked flames
- watch teacher demonstrations carefuly
- make sure room is well ventilated
what are common safety precautions for handling hazardous substances?
- safety screens
- wearing gloves
- eye protection
- washing hands after handling chemicals
- working in fume cupboard
what is a group?
vertical column of elements that have similar properties
what do group 1 elements include?
- lithium
- potassium
- sodium
what is the relationship between the group # and # of electrons?
group # corresponds to # of electrons in outer shell of atom
group 1 elements have 1 electron in outer shell
group 7 elements have 7 electrons in outer shell
what is a period?
horizontal row of elements
what are examples of elements in the same period?
- lithium
- neon
- carbon
what are the steps to write a balanced equation?
1) write word equation
2) substitute formulae for names of elements/compounds involved
3) balance equation by adding # in front of reactants/products
4) write balanced symbol equation
what is the name of group 1?
alkali metals
what happens if you go further an element down the group?
- higher reactivity
- lower melting and boiling points
- higher density
what is the trend in group 1 metals?
have 1 electron in outer shell
more reactive down group
what should you do when working with group 1 metals?
- use small amounts of metals
- safety glasses
- watch teacher demonstrations carefully
- ensure metals stored under oil
- avoid working near naked flames
what do alkalis react to form?
compounds
what do alkali metals look like?
shiny when freshly cut, but tarnish in moist air, go dull and become covered in metal oxide
how do alkali metals react with chlorine?
vigorously to form white crystalline salts
whats the general equation where M refers to the alkali metal?
2M + Cl2 —> 2MCl
eg
lithium + chlorine —> lithium chloride
2Li + Cl2 —> 2LiCl
what do alkali metals react with water to form?
metal hydroxide and hydrogen gas, mh dissolves in water to form alkaline solution:
2M + 2H20 —> 2MOH + H20
eg:
potassium + water —> potassium hydroxide + hydrogen
2K + 2H20 —> 2KOH + H2
what are examples of reactivity of alkali metals increasing further down a group?
- lithium, reacts quickly, water
- sodium, reacts vigorously, water + melts
- potassium, reacts vigorously, water that sparks produce
what is the names of group 7?
halogens
what can you use halogens for?
- bleach dyes
- kill bacteria in water
at room temp and pressure, what happens?
chlorine = green gas bromine = brown liquid iodine = dark purple solid
what do all halogens consist of?
diatomic molecules
only exist in pairs of atoms
halogens react with alkali metals to produce water?
give an example
halides
lithium + chloride —> lithium chloride
2Li + Cl2 —> 2LCl
what is the trend in group 7?
7 electrons in outer shell
less reactive going down group
what should you do when working with halogens?
- safety glasses
- work in fume cupboard
- use small amounts of dilute conc
- room = ventilated
what are ions?
atoms that’ve gained/lost electrons
as # of protons + electrons not equal, ions have overall charge
what is ionic bonding?
occurs between metal + non metal
electrons transfer from 1 atom to another to form electrically charged ions how?
- atoms that lose electrons become positively charged ions
- atoms that gain electrons become negatively charged ions
compounds of group 1 and 7 elements are what?
ionic compounds (salts).
- IC form crystals bc irons arranged into regular lattice
what happens to ionic crystals when they melt/dissolve in water?
they conduct electricity –> bc charged ions are free to move around
what is inside an atom?
has nucleus made up of protons and neutrons surrounded by electrons in shells
what do all protons and atoms have?
atom:
- same # of protons as electrons so atom is neutral
- atoms of same element have same # of protons
proton:
- same mass as neutron, mass of an electron is negligible
what does the electron configuration of an atom show?
how electrons are arranged in shells around the nucleus
what is spectroscopy?
when elements are heated, they emit distinctive coloured flames
light emitted produced line spectrum
each element, own spectrum
study of spectra used to analyse unknown substances + discover new elements eg helium —> first seen in light from sun
what are the colours of elements when heated?
sodium - yellow
potassium - lilac
lithium - red
how do you write a balanced equation?
follow these steps…
1) write word equation
2) substitute formulae
3) balance by adding #
4) write balanced equation
how do halogens react with other elements?
form compounds
reaction with alkali metals highly exothermic forming ionic compounds
eg:
lithium + bromine —> lithium bromide
2Li + Br2 —> 2LiBr
what is the displacement reactions of halogens?
reactive halogen displace less reactive halogen from an aqueous solution of its salt meaning chlorine will displace both bromine and iodine, while bromine will displace iodine
eg:
potassium iodide + chlorine —> potassium chloride + iodine
2Kl + Cl2 —> 2KCl + l2
what are the properties of compounds of halogens with alkali metals?
compounds of alkali metals and halogens conduct electricity when molten or dissolved in water
made up of ions
what are ionic compounds?
electrically neutral substances that have positive and negative charge
what is the history of the periodic table?
Dobereiner said some elements with similar properties formed groups of 3 - triads eg lithium, sodium and potassium
Newlands said when elements were arranged in order of increasing atomic weight, some repeating patterns in properties could be seen - law of octaves
Mendeleevs table allowed similar elements to be grouped together and show repeating patterns
- left gaps in table for non discoveries
what is the table of atom particle?
atom particle relative mass relative charge
p 1 +1
n 1 0
e nearly 0 -1
what are elements?
made of only 1 kind of atom, all atoms of an elements have same number of protons
diff elements have diff proton numbers and arranged in a order of increasing proton number in the pt giving repeating patterns in properties of elements
what happens when lithium, potassium and sodium react with cold water?
- float due to low density
- produce bubbles of hydrogen gas
