atomic structure

• What have scientists developed over time regarding atoms?

  New atomic models
• What did John Dalton propose about matter in 1803?

  All matter is made of tiny particles called atoms
• What did Dalton imagine atoms to be like?

  Tiny spheres that could not be divided
• Who discovered the electron and when?

  J J Thomson in nearly 1900
• What is the plum pudding model of the atom?

  An atom is a ball of positive charge with negative electrons embedded in it
• What experiment did Ernest Rutherford design in 1909?

  An experiment to test the plum pudding model
• What did Rutherford's experiment with alpha particles reveal?

  Most alpha particles went straight through the foil, but some were scattered
• What model did Rutherford propose after his experiment?

  The nuclear model of the atom
• What are the key features of the nuclear model?

  The mass of an atom is concentrated at its nucleus, which is positively charged
• How did Niels Bohr adapt Rutherford's nuclear model?

  He suggested that electrons orbit the nucleus in shells
• What did further experiments reveal about the nucleus?

  The nucleus contains small particles called protons
• Who discovered neutrons and when?

  James Chadwick in 1932
• What is the structure of an atom?

  An atom has a central nucleus surrounded by electrons arranged in shells
• How does the size of the nucleus compare to the atom?

  The nucleus is tiny compared to the atom as a whole
• What is the radius of an atom?

  About $0.1 \text{ nm} (1 \times 10^{-10} \text{ m})$
• What is the radius of a nucleus?

  About $1 \times 10^{-14} \text{ m}$
• How does the radius of a nucleus compare to the radius of an atom?

  The radius of a nucleus is less than $\frac{1}{1000}$ of the radius of an atom
• What are the subatomic particles found in the nucleus?

  Protons and neutrons
• What is the relative mass of a proton?

  1
• What is the relative mass of a neutron?

  1
• What is the relative mass of an electron?

  Very small
• Where is most of the mass of an atom concentrated?

  In its nucleus
• What is the atomic number of an element?

  The number of protons in an atom of that element
• How does the atomic number relate to different elements?

  Atoms of different elements have different numbers of protons
• What does it mean for an atom to have no overall electrical charge?

  It contains equal numbers of protons and electrons
• What is the atomic number of sodium?

  11
• What is the mass number of an atom?

  The total number of protons and neutrons in an atom
• Can atoms of different elements have the same mass number?

  Yes, atoms of different elements can have the same mass number
• How can the symbol for an atom be written?

  With its mass number at the top and atomic number at the bottom
• How do you calculate the number of protons in an atom?

  By using the atomic number
• How do you calculate the number of neutrons in an atom?

  By subtracting the atomic number from the mass number
• What are isotopes?

  Atoms of the same element with different numbers of neutrons
• What do isotopes of an element have in common?

  The same atomic number
• What is the significance of the number of electrons in isotopes?

  It determines their chemical properties
• What is the most abundant isotope of hydrogen?

  Hydrogen-1
• How is an isotope named?

  After the element and the mass number of its atoms
• What is the relative atomic mass of an element?

  A weighted average of the masses of the atoms of the isotopes
• How are relative atomic masses represented?

  With the symbol Ar
• What is the difference between mass numbers and relative atomic masses?

  Mass numbers are whole numbers, while relative atomic masses are not
• Why is the relative atomic mass of chlorine 35.5?

  Because chlorine contains two different isotopes