Atomic Structure

What is an atom?

An atom is the smallest part of an element that retains the properties of that element.

Daltons atomic theory

All matter is made of atoms

Atoms are indivisible

Atoms of different elements have different weights

What did Crookes do

Discovered cathode rays

what did Thomson discover

Discovered the electron and that electrons are negatively charged

Explain thomsons plum pudding model

Sphere of positive charge with negative electrons embedded randomly

What did Rutherford propose

The nuclear model of an atom.

Describe Rutherfords experiment

They fired alpha particles at a thing gold foil.

A fluorescent screen was placed around to detect where the alpha particles would go

Expectated results of Rutherford experiment

Alpha particles should pass through gold foil undeflected or minor deflections. this is because atoms are mostly empty space

Unexpected results of Rutherford experiment

Some alpha particles took large deflections. positive charge must be concentrated in one area and positive alpha particles that come close to it are being repelled.

Completely unexpected results of Rutherfords experiment

Tiny number of particles completely rebounded. Positively charged area must be dense and alpha particles that strike it get rebounded. Positive area must be small if only a tiny number of alpha particles collide with it.

What is positive charge and core called in rutherford nuclear model

Postive charges called protons and small, positive, dense area called the nucleus

Assumptions of the nuclear model

1. Atoms contain small, positive, dense, core called the nucleus.

2. Protons are in the nucleus

3. Atom is mostly empty space

4. Electrons around the nucleus in electron cloud

Limitations of the nuclear model

1. If nucleus contains positive protons, why does the nucleus not break apart.

2. If electrons are negatively charged, why do electrons not spiral into the nucleus

3. Electrons are in electron cloud, no description of how they are arranged.

What did Bohr describe?

Describes how electrons orbit the nucleus in energy levels

What happens when white light is passed through prism

Different frequencies are separated into a spectrum, it is called a continuous spectrum.

Bohr experiment- The hydrogen line emission spectrum

Bohr passes electricity through hydrogen gas and observed a pale purple colour.

He passed the colour through a prism

Observed four distinct coloured lines; red, green, blue-violet and violet this is called a line emission spectrum

Led Bohr to the idea that electrons orbited nucleus in these energy levels

Define energy level

Fixed amount of energy of an electron in an atom.

Why cant electrons be in between energy levels

Electrons cannot be in between energy levels because they aren’t stable

How can energy be given to electrons in atoms

Heating the atoms

Passing electricity through atoms

What is meant by the ground state of an atom

All electrons occupy the lowest available energy levels. Ground state is the most stable state.

What is meant by the excited state of an atom

Electrons absorb enough energy to transition up to higher energy levels. This is not stable for an atom, electrons will transition back down and release energy as a photon of electromagnetic radiation

What is a photon?

A Photon is a packet of electromagnetic radiation,

Visible light electromagnetic radiation spectrum

Gamma rays, X-rays, UV, infrared, radio waves

How do electrons effect frequency of photons

Larger the transition of electron, the greater the frequency of photon released

Formula of transiton of electrons and frequency of radiation

Em-En=hf

Higher energy level- lower energy level= frequency of photon