Atomic StructureSpectra of Science

Miss Amole

By PresenterMedia.com

• Simplest unit in an element• Determines the properties of that element

• “atom” is derived from a Greek word meaning “unable to be divided”

• Contains 3 subatomic particles: protons, neutrons, and electrons

What is an atom?

•PROTON: •Positively charges• Located in nucleus•Have mass

Subatomic Particles

• NEUTRON:• Neutral = no charge• Located in the nucleus• Have mass

Subatomic Particles

• ELECTRON:• Negatively charged• No mass (negligible)• Very fast; impossible to pin point exact location, speed, and direction

• Located outside nucleus in electron cloud

• Electron cloud contains energy levels

• Energy levels contain orbitals

Subatomic Particles

• The valence electrons an atom has determines reactivity• Valence electrons are those located in the outermost shell or energy level

• Each energy level can only hold a certain number of electrons

More About Electrons

• The number of protons and electrons an atom has is unique to each element• That is to say, every element has a different number of protons in its atom

• Coincides with the atomic number• Even though atoms contain charged particles, they are electrically neutral• That is to say an atom has an equal amount of protons and electrons

• Atoms contain mostly empty space• If the nucleus of an atom was the size of a marble, the entire

element would be the size of a football field

More About Atoms

• Democritus• Fourth century BC Greek philosopher• First to suggest the existence of atoms • Believed universe contained these invisible units that caused changes in matter• Believed atoms were indivisible

Development of Atomic Theory

• John Dalton• 1808 English schoolteacher• Suggested all atoms of a given element were alike• Believed different atoms could join together to form compounds• His theories are considered the foundation for modern atomic theory

Development of Atomic Theory

• Niels Bohr• 1913 Danish scientist• Suggested electrons move in set paths around nucleus that determine their energy level• Believed electrons would have to gain energy to move to a higher energy level or lose enregy to move down

Development of Atomic Theory

• By 1925, Bohr’s model no longer explained electron behavior• Current thought suggested electrons are act more like waves on a vibrating string than particles• Impossible to detect an electrons exact location, speed, or direction

Development of Atomic Theory

• Ions• Cations

•Created when an atom loses one or more electrons and becomes positively charged

• Anions•Created when an atom gains one or more electrons and becomes negatively charged

• Isotopes• Atoms of the same element with a different number of neutrons

Other Forms of Atoms

-Atomic Structure Video-Atom Builder