RCI - 1.1 A - Developing Atomic Theory 2024-25 S1B PDF

1.1 A The Nature of Atoms - Theories Read 1.1A, pg 10 and 11 What is an Atom? All matter consists of atoms. Atoms are the smallest part of an element that has all of the element’s properties. Atoms consist of three particles that are referred to as the subatomic particles. Atomic...

1.1 A The Nature of Atoms - Theories Read 1.1A, pg 10 and 11 What is an Atom? All matter consists of atoms. Atoms are the smallest part of an element that has all of the element’s properties. Atoms consist of three particles that are referred to as the subatomic particles. Atomic theory – study of the nature of atoms and how they combine Three Sub-Atomic Particles PROTON: positively charged; similar mass to neutron NEUTRON: no charge; similar mass to proton ELECTRON: negatively charged; very small mass compared to protons and neutrons The 2,400-year search for the atom…. https://www.youtube.com/watch?v=xazQRcSCRaY  400 BCE Democritus Atom – the smallest piece of matter that is indivisible. Elements on the periodic table represent individual atoms Did you know? In 400 BCE Democritus came up with the name after the Greek word “atomos” which means “cannot be cut” John Dalton’s “Billiard Ball” 1803 Revised Democritus idea of an atom: All matter is made up of tiny, indivisible particles (called atoms) All atoms of an element are identical Atoms of different elements behave differently Atoms can be re-arranged to form new substances in a Missing: Dalton was NOT chemical reaction able to explain charge. JJ. Thompson’s 1897 “Chocolate Chip Cookie” Discovered the electron which is a negatively charged particle Concluded that atoms were a positively charged sphere, with electrons spread throughout JJ. Thompson’s “Chocolate Chip 1897 Cookie” Thompson experimented with a cathode ray tube and discovered the first subatomic particle: the electron Since the beam was attracted to the positive plate, he knew the particles must be negatively charged Thomson's Cathode Ray Tube Experiments - YouTube Pause! Learning Check. 1. Draw a picture of an atom, showing some protons, neutrons and electrons. 2. What was Dalton’s model of the atom? 3. What new particle was introduced in Thomson’s model? How did they know this particle was present?  1911 Rutherford’s Experiment HYPOTHESIS RESULTS CONCLUSION Rutherford's Experiment: Nuclear Atom - YouTube Rutherford's Model of the Atom 1911 The center of an atom contains a dense positively charged nucleus The nucleus is surrounded by a cloud of negatively charged electrons Most of an atom is empty space Missing: Protons were determined to have a high atomic mass but did not account for the entire mass of an atom. Rutherford predicted there could be a third particle type. Niels Bohr 1913 Refined Rutherford’s model: Electrons orbit the nucleus with a defined amount of energy Electrons can jump to and from orbits, which results in a change of energy Orbit # of Each orbit can hold a 1 electrons 2 maximum number of 2 8 electrons. 3 8 (18) 4 8 (32) Subatomic Particles 1932 James Chadwick further investigated the atom to confirm the properties of the three types of subatomic particles: Electron (e-) Proton (P+) Neutron (no) Charge Negative Positive Neutral Inside Inside Location Orbit Nucleus Nucleus Nucleus Relative Mass 0.0005 amu 1 amu 1 amu Electrons effectively have no mass! The mass of an atom is determined almost entirely by the number of protons and neutrons Other contributions to our understanding of the atom... 1900 AD 700 AD 1700 AD 2000 2017 ← Want to learn more? And More!