The Structure of The Atom Atom An atom

The Structure of The Atom Atom An atom

The Structure of The Atom Atom An atom is the smallest particle of an element that retains the chemical properties of that element. Atoms consist of two regions. The nucleus is at the center of the atom and contains at least one positively charged particle called a proton and one

or more neutral particles called neutrons. electron neutron proton Surrounding the nucleus is a region occupied by negatively charged particles called electrons (this region is very large compared to the nucleus.

Protons, neutrons, and electrons are usually referred to as subatomic particles. electron neutron proton Discovery of the Electron The discovery of the electron occurred in the late

1800s when scientists were investigating the relationship between electricity and matter. The experiments were carried out in cathode-ray tubes. Cathode-Ray Tube A simple cathode-ray tube. Particles pass through the tube from the cathode, the metal disk connected to the

negative terminal of the voltage source, to the anode, the metal disk connected to the positive terminal. The experiments carried out by Joseph John Thomson in 1897, showed the particles that composed the cathode ray were negatively charged.

Thomson also thought that atoms must contain some positive charge. Thomson suggested that an atom consisted of a cloud of positive charge with the negative electrons embedded in it. This model is often called the plum-pudding model. Watch video clip. In 1909 experiments conducted by Robert

A. Millikan showed that atoms were electrically neutral and must contain a positive charge to balance the negative electrons. They also showed that atoms must contain other particles that account for most of their mass. Watch video clip. Discovery of the Atomic Nucleus In 1911 Ernest Rutherford, Hans Geiger, and Ernest

Marsden bombarded a thin piece of gold foil with fast-moving alpha particles. Some particles were redirected back toward the source. Rutherford concluded that this was caused by a densely packed bundle of matter with a positive charge (nucleus). Zinc sulfide screen Lead block

Thin gold foil Radioactive substance path of invisible -particles particles Most particles passed through. So, atoms are mostly empty. Some positive -particles particles deflected or bounced back!

Thus, a nucleus is positive & holds most of an atoms mass. Composition of the Atomic Nucleus The nuclei by atoms of different elements differ in the number of protons they contain (the number of protons in an atoms nucleus determine the atoms identity. If protons are positively

charged how does the nucleus stay together? Nuclear Forces!! When two protons are extremely close to each other, there is a strong attraction between them. A similar attraction exists when neutrons are very close to each other or when protons and neutrons are very close together. These short-range proton-neutron, proton-proton, and neutron-neutron forces hold the nuclear particles together

and are referred to as nuclear forces. Nuclear Forces The Sizes of Atoms The sizes of atoms are expressed in picometers ( 1 pm = 1 x 10-12 m). To get an idea of how small a picometer is, consider that 1 cm is the same fractional part of 103 km (about 600 miles) as 100 pm is of 1 cm.

Atomic radii range from about 40 to 270 pm.

Recently Viewed Presentations

  • Energy Systems - St Johns PE A-Level

    Energy Systems - St Johns PE A-Level

    At the 2008 Beijing Olympic Games, David Davies won the silver medal in the swimming 10 kilometre marathon event, in a time of 1 hour 51 minutes and 53.1 seconds.Explain how the majority of energy used during the race would...
  • Hazardous Waste Exclusions and Exemptions

    Hazardous Waste Exclusions and Exemptions

    A hazardous waste which is generated in a product or raw material storage tank, a product or raw material transport vehicle or vessel, a product or raw material pipeline, or in a manufacturing process unit or an associated non-waste-treatment-manufacturing unit,...
  • At Three Years, Opinion On ACA Remains Divided

    At Three Years, Opinion On ACA Remains Divided

    A budget reconciliation measure allows for changes in taxes and spending with a 51 vote majority in the Senate, but it cannot make changes to federal law that have only incidental effects on the ...
  • WELCOME TO THE DSO ORIENTATION WELCOME TO THE

    WELCOME TO THE DSO ORIENTATION WELCOME TO THE

    Employment support / volunteers and Employment preparation : Typically these programs offer a 1:9 or higher staff to individuals ratio , these individuals will usually need to be able to access the TTC and learn new routes with minimal support....
  • LWW PPT Slide Template Master

    LWW PPT Slide Template Master

    Assumption: Cultures guide the way people structure their experiences. Ethnography (cont.) Seeks an emic perspective (insider's view) of the culture Relies on wide range of data sources (interviews, observations, documents; some may be quantitative.) Participant observation is a particularly important...
  • Severe Acute Respiratory Syndrome - Penn State York

    Severe Acute Respiratory Syndrome - Penn State York

    SARS stands for Severe Acute Respiratory Syndrome. The virus is a "SARS-associated coronavirus (CoV)". ... Animals that the virus could possibly be adapted from include the Himalayan palm civets found in food markets and consumed as a delicacy in the...
  • Erik Arneson, Executive Director Right to Know Law

    Erik Arneson, Executive Director Right to Know Law

    that documents a transaction or activity of an agency . AND. is created, received, or retained pursuant to law . OR. in connection with a transaction, business or activity of an agency." Right to Know for Local Govt Webinar as...
  • IIMB Hostel block 7 ( 16 rooms) Block

    IIMB Hostel block 7 ( 16 rooms) Block

    Wood shavings, rock wool, oil rags, and other inflammable materials are removed from site daily? only industrial gas cylinders used and stored in appropriate manner (No cooking gas)? new gas tubes with proper cover used for welding? Do hoists, cranes...