10. Concepts in Chemistry: The Atom Flashcards
What is the theory of Atomic Structure?
John dalton (start of 19th century) - atoms as solid spheres - different spheres made up different elements - (solid sphere model)
JJ Thompson (1897) - concluded that atoms weren’t solid spheres - measurements of charge and mass showed atoms contain smaller negatively charged particles called electrons - (plum pudding model)
How did Rutherford show that the Plum Pudding Model was wrong?
1909, Rutherford, Geiger and Marsden - Gold foil experiment - fired positively charged alpha particles at very thin sheet of gold
Plum pudding model meant they expected the particles to pass straight through the sheet or slightly deflect because positive charge of each atom was though to be spread out through the pudding of the atom
Most of particles went straight through - some deflected more than expected - some deflected backwards - showing that the plum pudding model couldn’t be right
Rutherford - theory of the nuclear atom - tiny positively charged nucleus at centre surrounded by cloud of negative electrons
Most of atom is empty space
What does the refined Bohr Model explain?
Bohr proposed that electrons were contained in shells
Only exist in fixed orbits or shells - each shell has a fixed energy
How are theories backed up by evidence?
Experiments - new evidence - theory of atomic structure modified
Scientific knowledge develops - new evidence prompts new ideas
Ideas used to make predictions which if proven correct show the ideas are right
Scientists put their ideas and research for peer review
What are Atoms and what do they contain?
Protons - heavy and positively charged
Neutrons - heavy and neutral charge
Electrons - hardly any mass - negatively charged
All substances are made from atoms
In atom, the number of protons = the number of electrons ie neutral or no charge unlike ions
What are Protons?
Protons contained in the nucleus and are positively charged and heavy
What is the Nucleus?
Middle of the atom
Contains protons and neutrons
Positively charges because of the protons
Almost all of the mass in atom is concentrated in the nucleus
Compared to overall size of atom, the nucleus is tiny
What is an Electron?
Move around the nucleus in electron shells
Negatively charged
Tiny but shells cover a lot of space
Size of the shells determine the size of the atom - atomic radius of about 10 to the -10m
Tiny mass - negligible
What is the Atomic Number?
Nuclear symbol of atom tells the atomic (proton) number and mass number
Atomic number - number of protons in an atom
Every atom of an element has same number f protons
For a neutral atom - number of protons = the number of electrons - number of electrons also = the atomic number
What is the Mass Number?
Mass number is total number of protons and neutrons in the atom
Determine number of neutrons by subtracting atomic number from the mass number
