Atomic Structure – Chapter 4 Studying Atoms – 4.1

Studying Atoms The philosopher Democritus believed that all matter consisted of extremely small particles that could not be divided. He called these particles atoms

Dalton’s Theory Dalton proposed the theory that all matter is made up of individual particles called atoms, which cannot be divided.

Dalton’s Theory All elements are composed of atoms All atoms of the same element have the same mass, and atoms of different elements have different masses Compounds contain atoms of more than one element In a particular compound, atoms of different elements always combine in the same way

Dalton’s Theory Atoms are a solid sphere

Thomson’s Model Thomson’s experiments provided the first evidence that atoms are made of even smaller particles Subatomic particles - protons, electrons, neutrons

Thomson’s Model “Plum Pudding” or “Cookie Dough”

Rutherford’s Atomic Theory According to Rutherford’s model, all of an atom’s positive charge is concentrated in its nucleus Nucleus – a dense, positively charged mass located in the center of the atom

Rutherford’s Atomic Theory

Homework Page 105 Questions 1-8 (don’t have to write out questions) *Keep these when finished*

The Structure of an Atom 4.2

Subatomic Particles Protons, electrons, and neutrons Can be distinguished by mass, charge, and location in an atom

Protons Found in the nucleus Positively charged Mass of 1 Symbol p+

Electrons Found outside of the nucleus - “cloud” Negatively charged Very small mass = 1/1836 Symbol e-

Neutrons Found in the nucleus Neutral - no charge Mass of 1 Symbol n

Atomic Number Number of protons in an element Atoms of different elements have different numbers of protons Also equals number of electrons because an atom has no charge - the positive and negative charges cancel each other out

Mass Number – Atomic Number Number of particles in the nucleus Protons + Neutrons Mass Number – Atomic Number = Number of Neutrons

Isotopes Atoms of the same element that have different numbers of neutrons and different mass numbers Have same atomic number because they are the same element

Carbon-13 & Carbon-12 are Isotopes 13 and 12 are their mass numbers Protons = Neutrons = Electrons = Carbon - 13

Modern Atomic Theory 4.3

Bohr’s Model Bohr’s model of the atom looks like a solar system Electrons move with constant speed in fixed orbits around the nucleus

Bohr’s Model

Energy Levels The possible energies that electrons in an atom can have An electron in an atom can move from one energy level to another when the atom gains or loses energy

Electron Cloud Model Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus

Electron Cloud Model

Electron Cloud Model

Atomic Orbitals Orbital – a region of space around the nucleus where an electron is most likely to be found An electron cloud is a good approximation of how electrons behave in their orbitals.

Electron Configurations The arrangement of electrons in the orbitals of an atom The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies – ground state

Homework – Questions Pg 121: 1-23 For 1-10 write out the questions and answers then circle the correct answer. 11-23 just find the correct answer