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Flashcards in The Periodic Table Deck (40)
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1

The Greeks

-Had idea that universe was made up of a few basic substances/elements
-Thought 4 elements were - earth, air, water, fire

2

Robert Boyle

-Gave first accurate definition of an element
-Described it as 'A simple substance that cannot be broken into anything simpler'

3

Humphrey Davy

-Discovered potassium by passing electricity through a compound of potassium
-Discovered sodium, calcium, barium, strontium, magnesium through same way

4

Johann Dobereiner

-Noticed that the 'atomic weight' (relative atomic mass) of bromine (80) was half way between that of chlorine (35.5) and iodine (127)
-Saw that there was smooth gradation of chemical properties from chlorine to bromine to iodine
-Observed similar pattern with calcium, strontium, barium among others - called triads
-Few other cases of this found but was earliest attempt to trace relationships between properties of elements and their weights

5

John Newlands

-Arranged elements in order of relative atomic mass
-Noticed properties of elements seemed to repeat with every 8th element

6

Problems with John Newlands' thing

-Did not realise some elements had not yet been discovered, left no gaps
-Tried to force all known elements to fit into table + his law of octaves work for only first 16, then some were forced into wrong groups
-Noble gases weren't discovered - properties in first 2 periods now repeat after every 9th element instead of eighth

7

Dimitry Mendeleev

-Arranged elements in order of increasing atomic mass too but placed elements with similar properties under each other in groups so every 8th element had similar physical + chemical properties

8

Mendeleev's Periodic Law

When elements are arranged in order of increasing atomic weight, properties of elements recur periodically
-Placed all elements w/ similar properties in same column
-Left gaps in table to make all known elements fit into proper group
-Predicted properties of undiscovered elements
-Reversed order of some elements to make properties fit columns

9

Henry Moseley

-Discovered method of determining number of protons in nucleus - called atomic number (by studying frequencies varied by number of positive charge in nucleus)
-Showed that if elements are arranged in increasing atomic number, not necessary to reverse order of some of elements; elements fall naturally into correct groups

10

Modern Periodic Law

When elements are arranged in order of increasing atomic number, properties of elements recur periodically i.e. properties displayed by an element are repeated at regular intervals in other elements

11

Mendeleev Periodic Table (vs Modern Periodic Table)

-Orders elements based on their atomic weight
-Had gaps for missing elements at that time
-Has 8 vertical columns called groups, 12 horizontal rows called periods
-Has elements with dissimilar properties in same group sometimes
-Doesn't support the fact of the existence of isotopes

12

Modern Periodic Table (vs Mendeleev Periodic Table)

-Orders elements based on their atomic number
-Has no concept for having gaps for missing elements at time
-Has 18 columns called groups, 7 rows called periods
-Have similar properties repeated at regular intervals
-Supports this fact as the classification is based upon atomic number

13

Alkali metals

-Easy to cut
-Are reactive w/ air (H2O content in air)
-Dull until cut
-Stored under oil
-Low melting + boiling points
-Low density

14

Alkaline earth metals

-Shiny
-Reactive due to readily losing their two outer electrons
-Low melting + boiling points
-Low density

15

Safety procedures for testing reactivity of alkali metals in water

-Goggles + labcoats worn by all present in room
-Protective screen set up in front of demonstration
-Laboratory tongs used to drop metals into bowl of water

16

Lithium + water

Very minor reaction, some fizzing giving off lithium hydroxide

Made Lithium Hydroxide + Hydrogen

17

Sodium + water

Produced major reaction with metal catching on fire & eventually exploding

Made Sodium Hydroxide + Hydrogen

18

Potassium + water

Reacted violently but less so than did sodium. Sparks observed flying out of bowl of water before it fizzed out

Made Potassium Hydroxide + Hydrogen

19

Element

Substance that cannot be split up into simpler substances by chemical means

20

Compound

Substance made up of 2 or more different elements combined together chemically

21

Atomic Number

Number of protons in nucleus of that atom

22

Mass Number

Sum of number of protons + neutrons in nucleus of an atom of their element

23

Halogens

-Non-metals
-Low melting + boiling points
-Chlorine + fluorine gases at room temp
-Bromine liquid at room temp
-Iodine + astatine solids at room temp
-Become less reactive as you go down group
-Kill bacteria
-Bleaching agents

24

Noble gases

-Unreactive/inert (due to full outer shell)
-Boiling points low, increase as you go down group
-Non-metals
-Colourless

25

Lithium + Water equation

Li + H2O = LiOH + 1/2 H2

26

Sodium + Water equation

Na + H2O = NaOH + 1/2 H2

27

Potassium + Water equation

K + H2O = KOH + 1/2 H2

28

how did Moseley show that Mendeleev's assumptions n his arrangements were correct, especially in the case of tellurium and iodine?

when arranged according to atomic number, tellurium is before iodine

29

why did Mendeleev place tellurium before iodine in his periodic table?

-chemical properties matched better in that order
-to ensure periodic recurrence of chemical properties
-elements with similar chemical properties were listed in columns/groups

30

how did Mendeleev predict properties of elements before they were discovered?

-Predicted properties from properties of elements in same group
/-predicted properties from properties of known elements