Atomic Structure

Objectives Explain Dalton’s atomic theory Explain Dalton’s atomic theory Be able to state the charge, mass, & location of each part of an atom Be able to state the charge, mass, & location of each part of an atom Be able to compare & contrast Bohr’s model with the modern model of the atom Be able to compare & contrast Bohr’s model with the modern model of the atom Explain orbitals, their structure, & valence electrons Explain orbitals, their structure, & valence electrons

History of Atoms The idea of the atom first came from a Greek philosopher Democritus nearly 2500 years ago The idea of the atom first came from a Greek philosopher Democritus nearly 2500 years ago It started with a set of simple questions, “If you take a piece of chalk and break it in half, are both halves still chalk? If you continue to divide each piece, is there a limit to the division before it becomes something else?” It started with a set of simple questions, “If you take a piece of chalk and break it in half, are both halves still chalk? If you continue to divide each piece, is there a limit to the division before it becomes something else?” Democritus thought there was a limit which he called atomos, meaning “unable to be cut” Democritus thought there was a limit which he called atomos, meaning “unable to be cut”

Models of the Atom Democritus Democritus John Dalton John Dalton Niels Bohr’s Niels Bohr’s

Democritus' Theory of Atoms 1.All matter consists of invisible particles called atoms. 2.Atoms are indestructible. 3.Atoms are solid but invisible. 4.Atoms are homogenous. 5.Atoms differ in size, shape, mass, position, and arrangement. He believed that the movements of atoms caused the changes in matter he observed However, he had no way of proving the existence of atoms

John Dalton’s Atomic Theory All matter consists of atoms 2.Atoms are indestructible & unchangeable 3.Elements are characterized by the weight of their atoms 4.In chemical reactions, atoms combine in small, whole number ratios 5.When elements react, their atoms may combine in more than one whole-number ratio

Characteristics of Atoms Are the building blocks of molecules Are the building blocks of molecules Smallest part of an element that still has the element’s properties Smallest part of an element that still has the element’s properties Unreacted atoms have no overall charge Unreacted atoms have no overall charge Atoms have 5 basic parts Atoms have 5 basic parts Atoms are made of protons, neutrons, & electrons (subatomic particles) Atoms are made of protons, neutrons, & electrons (subatomic particles) The protons & neutrons are housed in the center of the atom in the nucleus The protons & neutrons are housed in the center of the atom in the nucleus Electrons are moving around outside of the nucleus within the electron cloud Electrons are moving around outside of the nucleus within the electron cloud

Atom Model

Subatomic Particles Protons have a __________ charge Protons have a __________ charge Neutrons have ___________ charge Neutrons have ___________ charge Electrons have a __________ charge Electrons have a __________ charge The number of protons and electrons for an atom is unique for each element. The number of protons and electrons for an atom is unique for each element.

Bohr’s Model of the Atom In 1913, Niels Bohr suggested that electrons in an atom move in set paths around the nucleus In 1913, Niels Bohr suggested that electrons in an atom move in set paths around the nucleus “Like planets in orbit” “Like planets in orbit” The path defines the electron’s energy level The path defines the electron’s energy level 1.Electrons can only be in certain energy levels 2.Electrons must gain energy to move to a higher energy level 3.Electrons must lose energy to move to a lower level

Bohr’s Model

Modern Atomic Model By 1925, Bohr’s model didn’t explain electron behavior By 1925, Bohr’s model didn’t explain electron behavior The new model proposed that electrons behave like waves on a vibrating string The new model proposed that electrons behave like waves on a vibrating string This is known as the “wave-particle duality of nature” This is known as the “wave-particle duality of nature” This model was developed by Louis de Broglie, Albert Einstein & Max Planck This model was developed by Louis de Broglie, Albert Einstein & Max Planck

Modern Atomic Model Modern Atomic Model An electron’s exact location can not be determined nor can its speed or direction An electron’s exact location can not be determined nor can its speed or direction Electrons are constantly moving Electrons are constantly moving To illustrate the location of electron we now use the electron cloud To illustrate the location of electron we now use the electron cloud Electrons still exist in energy levels Electrons still exist in energy levels The number of filled energy levels depends on the number of electrons The number of filled energy levels depends on the number of electrons

Energy Levels 1 st energy level = 2 electrons 1 st energy level = 2 electrons 2 nd energy level = 8 electrons 2 nd energy level = 8 electrons 3 rd energy level = 18 electrons 3 rd energy level = 18 electrons 4 th energy level = 32 electrons 4 th energy level = 32 electrons For example: Na has 11 electrons For example: Na has 11 electrons 2 in level 1 2 in level 1 8 in level 2 8 in level 2 1 in level 3 1 in level 3

Orbital Theory Electrons are found in orbitals within energy levels Electrons are found in orbitals within energy levels Within each level, electrons occupy orbitals that have the lowest energy Within each level, electrons occupy orbitals that have the lowest energy 4 different kinds of orbitals 4 different kinds of orbitals s p d f

s Orbitals Are the simplest Are the simplest Are spherical in shape Are spherical in shape Have the lowest energy Have the lowest energy Hold only 2 electrons Hold only 2 electrons

p Orbitals Are dumbbell shaped Are dumbbell shaped They can be oriented three different ways in space They can be oriented three different ways in space Has more energy than a s orbital Has more energy than a s orbital Each p orbital can hold 2 electrons for a total of 6 electrons Each p orbital can hold 2 electrons for a total of 6 electrons

p Orbitals

d & f Orbitals Are much more complex Are much more complex There are 5 possible d orbitals There are 5 possible d orbitals There are 7 possible f orbitals There are 7 possible f orbitals f orbitals have the greatest energy f orbitals have the greatest energy Each orbital holds a maximum of 2 electrons Each orbital holds a maximum of 2 electrons

d Orbitals

f Orbitals

Relationship between Levels 1 st energy level has 1 sublevel = s 1 st energy level has 1 sublevel = s So it contains 1 orbital and holds 2 electrons 2 nd energy level has 1 s orbital and 3 p orbitals 2 nd energy level has 1 s orbital and 3 p orbitals So it can hold 8 electrons 3 rd energy level has s, p, & d orbitals 3 rd energy level has s, p, & d orbitals So it can hold 18 electrons 4 th energy level has s, p, d, & f orbitals 4 th energy level has s, p, d, & f orbitals So it can hold 32 electrons

Valence Electrons Every atom has between 1 and 8 valence electrons Every atom has between 1 and 8 valence electrons Valence electrons are electrons in the outermost energy level of an atom Valence electrons are electrons in the outermost energy level of an atom They determine an atom’s chemical properties and its ability for form bonds They determine an atom’s chemical properties and its ability for form bonds For example: Neon For example: Neon Has 10 electrons 2 electrons in the lowest level 8 electrons in the 2 nd level Thus, it has 8 valence electrons!

Quantum Model