As children move towards middle and late childhood, the relationship between physical activity and motor skill competence evolves and strengthens (Stodden et al. 2008). During middle childhood, a childâs perceived motor competence more closely estimates their actual motor skill competence.
In 1842 Gustav Mosander separated yttria, found in the mineral gadolinite, into three fractions which he called yttria, erbia, and terbia. The names erbia and terbia became confused in this early period. After 1860, Mosander's terbia was known as erbia, and after 1877, the earlier known erbia became terbia. The erbia of this period was later shown to consist of five oxides, now known as erbia, scandia, holmia, thulia and ytterbia.
Barium was first isolated in 1808 by English chemist Sir Humphry Davy (1778-1829). In 1807 and 1808, Davy also discovered five other new elements: sodium, potassium, strontium, calcium, and magnesium.arium had first been identified as a new material in 1774 by Swedish chemist Carl Wilhelm Scheele (1742-86). The form with which Scheele worked, however, was a compound of barium, barium sulfate (BaSO 4). Barium sulfate is, in fact, the most common naturally occurring ore of barium.