1. Atomic structure & The periodic table (history of the atom and development of periodic table Flashcards
How did elements used to be grouped?
In order of atomic mass
When was the periodic table first created?
- In 1869, Dimitri Mendeleev arranged the 50 known elements into a table
How did Mendeleev group elements together?
He grouped them by similiar reactivities and properties
Why did Mendeleev leave gaps?
for undiscovered elements
What happened after Mendeleev left gaps in his periodic table?
- the elements were later discovered
- the elements that were found fitted with the trends he predicted them to have
How is the periodic table now grouped and why?
- In order of atomic number
- because in the early 20th century isotopes were discovered, further proving they couldn’t be ordered in order of atomic mass
Now what does each group and period represent?
- Groups: how many electrons are on valence shell
- Periods: amount of shells in each atom
What group are the Alkali metals?
Groups 1 and 2
What group are the Halogens?
Group 7
What group are the Noble gases?
Group 0
What did John Dalton (early 1800s) theorise?
- that atoms were spherical balls that were nothing else
- that each element would have a different type of atom
What did JJ.Thompson discover?
- He discovered the electron inside atoms
- He thought atoms were a cloud of positive charge with electrons embedded inside the atom (like the raisins in a plum pudding)
Who came up with the Plum Pudding Model?
JJ. Thompson
When did JJ Thompson discover the electron?
1897
How and who proved the Plum pudding model as wrong?
Rutherford, through the Alpha particle scattering experiment
What was the Alpha particle scattering experiment?
- Rutherford and Marson fired alpha particles at a thin sheet of gold
- they were expecting the particles to travel straight through and some to be deflected
What were the observations and conclusions of the Alpha particle scattering experiment?
- Observation: most went straight through
- Conclusion: most of the atom is empty space
- Observation: some deflected less than 90 degrees
- Conclusion: the nucleus is positively charged
- Observation: few deflected more than 90 degrees
- Conclusion: most of the mass is concentrated in the nucleus
What is an alpha particle?
a positively charged particle
When was the Alpha particle scattering experiment?
1909
What did James Chadwick discover?
He discovered the neutron via the use of isotopes
What did the nuclear model propose?
- mass of the atom was concentrated in the nucleus
- the nucleus was charged
Who adapted the nuclear model of the atom?
Niels Bohr
How did Bohr adapt the nuclear model
- by suggesting that electrons orbit the nucleus
- and that electrons orbit the nucleus in fixed shells, with each shell at a fixed distance from the nucleus
What resulted in the creation of the Nuclear model?
Rutherford and Marson’s alpha particle scattering experiment
What is this model of the atom called?
The Nuclear Model
What is this model of the atom called?
The Bohr Model
3 features of the plum pudding model?
- the atom is a positively charged ‘dough’
- negative electrons are distributed throughout the atom
- the mass of the atom is evenly distributed
3 features of the Nuclear Model?
- the atom is mostly empty space
- negative electrons orbit the nucleus at a distance
- almost all of the mass of the atom is concentrated in the positively charged nucleus
Who proposed the Nuclear Model of the atom?
Rutherford
