Energy in Electrons NOTES

Reminders Lab Equipment Quiz – Wednesday (not Tues.) Daily Warm-up Questions will come from what we have already covered in class. This week will be based on Matter Review Packet.

I. Energy and Electrons A.Energy comes in many forms: HEAT (thermal) LIGHT (radiant) MOTION (kinetic) ELECTRICAL CHEMICAL NUCLEAR ENERGY GRAVITATIONAL

B.Electrons are located in clouds (called orbitals) surrounding the nucleus of an atom. 1. Each orbital is a specific distance from the nucleus (we call this the energy level). 2. Electrons are found in different energy levels based on the amount of energy they have.

C.We learned that electrons are going to be found 1. When electrons are found in the lowest energy level possible we say they are in the ground state. Ground state – state in which all electrons in an atom have the lowest possible energies

2. Electrons can absorb energy from their environment and then move to higher energy levels and be in an excited state. Excited State – state in which one electron moves to an orbital in a higher energy level

II. Electromagnetic Radiation and Emission Spectra A. Electrons in an excited state are unstable which means they won’t stay at the higher energy levels very long. When the electrons go back to the energy level they must release the energy they absorbed, usually in the form of light.

B.Light energy is made up of waves and is a type of electromagnetic radiation. Electromagnetic radiation – energy in the form of electromagnetic waves that travel in a vacuum at a speed of x 10 8 m/s.

1. Waves have two important characteristics: wavelength and frequency. Frequency – the number of wave cycles that pass a given point per unit of time Wavelength – the distance between adjacent crests of a wave

2.Different waves of light will have different amounts of energy in them based on their wavelength and frequency. Waves with a high frequency have small wavelengths and higher energy. Waves with a lower frequency have larger wavelengths and less energy.

C.The amount of energy excited state electrons release as they go back to being ground state electrons depends on the energy level of the excited state electrons. 1. A larger distance between energy levels, the more energy that is released.

2. Electrons of different atoms of different elements will go to different energy levels when in an excited state. a. This means they will give off different frequencies of light.

b.These frequencies occur in predictable patterns for each element called atomic emission spectra. Emission spectra – the pattern formed when light passes through a prism or diffraction grating to separate it into different frequencies of light it contains.

Evidence for Energy Levels Bohr theorized that electrons absorbed energy and moved to higher energy states. Then, these excited electrons gave off that energy as light waves when they fell back to a lower energy state. Atomic Structure: Basic Concepts

Evidence for Energy Levels These regions of space in which electrons can move about the nucleus of an atom are called energy levels. Because electrons can have only certain amounts of energy, Bohr reasoned, they can move around the nucleus only at distances that correspond to those amounts of energy. Atomic Structure: Basic Concepts

The Electron Cloud Model Instead, they are spherical regions of space around the nucleus in which electrons are most likely to be found. As a result of continuing research throughout the 20th century, scientists today realize that energy levels are not neat, planetlike orbits around the nucleus of an atom. Atomic Structure: Basic Concepts

The space around the nucleus of an atom where the atom’s electrons are found is called the electron cloud. The Electron Cloud Model These spherical regions where electrons travel may be depicted as clouds around the nucleus. Electrons themselves take up little space but travel rapidly through the space surrounding the nucleus. Atomic Structure: Basic Concepts

The Electron Cloud Model Atomic Structure: Basic Concepts

Electrons in Energy Level Each energy level can hold a limited number of electrons. How are electrons arranged in energy levels? The lowest energy level is the smallest and the closest to the nucleus. Atomic Structure: Basic Concepts

Electrons in Energy Level The second energy level is larger because it is farther away from the nucleus. It holds a maximum of eight electrons. This first energy level holds a maximum of two electrons. The third energy level is larger still and holds a maximum of 18 electrons. Atomic Structure: Basic Concepts

Energy Levels A hydrogen atom has only one electron. It’s in the first energy level. Atomic Structure: Basic Concepts