Arrangement of electrons in atoms Chapter 4 Arrangement of electrons in atoms

New atomic model section 1 so far, we have three atomic models Dalton Thomson Rutherford

Properties of light All forms of electromagnetic radiation make up the electromagnetic spectrum. Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space.

Electromagnetic spectrum

Properties of light

𝜆 Properties of light Wavelength The distance between corresponding points on adjacent waves Unit of measurement of wavelength is a distance measurement, could be in any meter measurement, meters, centimeters, nanometers

Properties of light Frequency V Is the number of waves that pass a given point in a specific time, usually one second.

Frequency ( v ) Unit of measurement is waves/second One wave/sec is called a hertz ( Hz)

Speed of light (c ) 3.0 x 108 m/s How fast is light?

A jet moving at a ground speed of 500 mph, crosses the U.S. in 4 hours A jet moving at the speed of light 30,000,000 m/s would travel around the equator of the Earth 7.5 times is a sec. Light travels at 186,000 mi/sec

Frequency and wavelength have a relationship Speed of light (c) = wavelength (𝜆) x frequency (v) C = 𝜆v To solve for 𝜆 : 𝜆 = 𝑐 𝑣 solve for v = 𝑐 𝜆

When wavelength decreases then frequency increases Frequency decreases when wavelength increases This is called an inverse relationship

Photoelectric effect This effect refers to the emission (release) of electrons from a metal when light shines on the metal. Packets of light called photons (particles of light) of a certain frequency can knock electrons off of a metal.

Go to web, show photoelectric phet

Light as a particle Max Planck was studying the emission of light from hot objects. He proposed that a hot object does not emit electromagnetic energy continuously, as would be expected if the energy was in the form of a wave. He suggested that the light was small packets of energy he called quanta.

Particles of light A quantum of energy is the minimum quantity of energy that can be gained or lost by an atom. Planck stated the following relationship between energy and the frequency of radiation E = hv

Particles of light E = hv E is energy in joules ( j ) this is a quantum of radiation. V is frequency in seconds ( s ) h is Planck’s constant. It is always 6.626 x 10-34 j/s h = 𝐸 𝑣 v = 𝐸 ℎ

A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. Einstein explained the photoelectric effect by proposing that electromagnetic radiation is absorbed by matter only in whole numbers of photons. In order for an electron to be ejected from a metal surface the electron must be struck by a single photon with a minimum energy required to knock the electron loose.

Line emission spectrum

Ground and excited state Ground state – is the lowest energy state of an atom Excited state – a state is which an atom has a higher potential energy than it has in its ground state.

Another atomic model Niels Bohr Working with hydrogen gas Came up with another atomic model The electrons orbit the nucleus of the atom in energy levels that are specific distances from the nucleus.

Bohr atomic model

Bohr’s atomic model Electrons exist in energy levels certain distances from the nucleus. Bohr’s model explains the behavior of electrons in hydrogen gas and other gases, with the release of energy as light

Atom is in ground state – energy, as a photon, is absorbed and the atom moves to excited state atom is in excited state – energy is emmited as light and the atom moves back to ground state

Now we have four atomic models Dalton Thomson Rutherford Bohr