Atomic structure Mrs. Meadows

What is the Atomic Theory? states that matter is composed of discrete units called atoms.

What is an atom? The smallest particle of an element that retains the properties of that element

Who took part in the atomic theory? Democritus Dalton Thompson Rutherford Bohr

When did the atomic theory start? 460 B.C.

Who is Democritus? Was the first scientist to suggest the existence of atoms

What did he discover? Democritus believed that Everything is composed of atoms Atoms are hard small particles Thought matter was made of tiny particles that could not be divided (indivisible)

Who is Dalton? In 1808 Dalton continued Democritus work He believed that -All matter is composed of atoms -atoms are indivisible (atoms are the smallest) -All atoms of an element are identical

What was wrong with Democritus and Daltons theory? Atoms can be subdivided into protons/Neutrons/ electrons

Who was the next guy? JJ Thompson (1856-1940)

What did Thompson propose? Discovered the electrons by the cathode ray experiment Came up with the Plum Pudding Model (Electrons are in a soup of positive charge)

What was wrong with Thompsons theory? Electrons and protons are not evenly disturbed through out the atom

Who was the next guy? Rutherford (1910)

What did Rutherford propose? -Nucleus theory Gold Foil Experiment Atoms have a large center mass that is composed of a positive charge -Atoms are mostly empty space -Electrons orbit randomly around nucleus

What is a nucleus? Central part of atom containing protons and neutrons

What was wrong with Rutherford's theory? Electrons do not orbit randomly around the nucleus

Who was the next guy? Neils Bohr (1885-1962)

What did Bohr propose? Planetary model (1913) Nucleus surrounded by orbiting electrons at different energy levels Electrons do not randomly orbit Electrons orbit like the solar system are the sun

Atomic Stucture https://www.youtube.com/watch?v=sRPejoNktKE

What are Subatomic Particles? Particles smaller than an atom Protons, neutrons, electrons

What are Protons? Positively charged subatomic particle Located in the nucleus

What are electrons? Negatively charged subatomic particle Located outside of nucleus

What are neutrons? Subatomic particle with no charge Located inside the nucleus

What Charge does atoms have? All atoms have the same number of protons and electrons Atoms want to be neutral Positive charge proton = negative charge electron

What subatomic particle determines the element? The proton! Build elements https://phet.colorado.edu/sims/html/build-an- atom/latest/build-an-atom_en.html

What are Neutral atoms? Elements that are neutral have the same number or protons, electrons, and neutrons. The number of protons = number of electrons Protons (+) charge and electrons (-) charge 4 protons and 4 electrons = 0 net charge

What is Bohrs Models?

What are electron shells? Each element has the same number of orbirts around the nucleus. Those orbits are called electron shells

How do we make a bohr model? 1) Determine the number of protons in nucleus Draw them in inner circle 2) Determine the number of electrons Place in orbits around the nucleus 1st orbit – 2e max 2nd orbit – 8e max 3rd orbit – 8e max

What are Valence Electrons? Valence electrons are electrons in the outer shell of an atom

Draw bohrs model for Boron 5 electron 2 in 1st shell and 3 in outershell

What is the atomic number? Is the number of protons in the atom. Number of protons = number of neutrons

What is the mass number Is the number of protons AND neutrons in the nucleus

Does every atom of the same element have the same # of neutrons? No, some atoms of the same element have different number of neutrons They are called isotopes Will result in a different mass number

What is an exmple of an isotope Carbon 12 and carbon 15 We put the mass number after the name of the element So carbon 12 has 6 protons and 6 neutrons So carbon 15 has 6 protons and 9 neutrons

How do we find the number of neutrons in an isoptope? N = neutrons N = atomic mass – atomic number N = (# of protons and neutrons) – ( # of protons)

Calculating average atomic mass given isotopes The element nitrogen has two isotopes with masses of 14(99.5%) and 15(0.5%). Calculate the average atomic mass of nitrogen

Your Turn The element chlorine has two isotopes with masses of 35 (75.5%) and 37 (24.5%). Calculate the average atomic mass of chlorine